Method for supporting handover in mobile communication network

ABSTRACT

The present disclosure relates to a pre-5th-Generation (5G) or 5G communication system to be provided for supporting higher data rates Beyond 4th-Generation (4G) communication system such as Long Term Evolution (LTE). According to embodiments, an access and mobility management function (AMF) comprises at least one transceiver; and at least one processor, wherein the at least one processor is configured to receive, a mobility management entity (MME) for an evolved node B (eNB), a message associated with a handover required message for an inter-system handover from an evolved packet system (EPS) to 5G system (5GS) with a secondary gNB (SgNB) used as a target next generation node B (gNB), wherein the SgNB and the target gNB are co-located and the eNB is associated with the SgNB in a dual connectivity; transmit, to the target gNB, a handover request message for the inter-system handover from the EPS to 5GS with the SgNB used as the target gNB; and receive, from the target gNB, an acknowledge of the handover request message. The handover required message includes an SgNB user equipment (UE) X2 application protocol ID (SgNB UE X2AP ID) for identifying a UE over X2 interface in the SgNB. The handover request message includes the SgNB UE X2AP ID, and the SgNB UE X2AP ID is allocated at the SgNB.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. § 119to Chinese Patent Application No. 201910667347.4, filed on Jul. 23,2019, in the Chinese Patent Office, Chinese Patent Application No.201911296462.1, filed on Dec. 16, 2019, in the Chinese Patent Office,and Chinese Patent Application No. 202010318866.2, filed on Apr. 21,2020, in the Chinese Patent Office, the disclosures of which areincorporated herein by reference, in their entireties.

BACKGROUND 1. Field

The present disclosure relates to the field of mobile communicationtechnologies, and in particular to a method for supporting handover in amobile communication network.

2. Description of Related Art

To meet the demand for wireless data traffic having increased sincedeployment of 4th generation (4G) communication systems, efforts havebeen made to develop an improved 5th generation (5G) or pre-5Gcommunication system. Therefore, the 5G or pre-5G communication systemis also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.

The 5G communication system is considered to be implemented in higherfrequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higherdata rates. To decrease propagation loss of the radio waves and increasethe transmission distance, the beamforming, massive multiple-inputmultiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna,an analog beam forming, large scale antenna techniques are discussed in5G communication systems.

In addition, in 5G communication systems, development for system networkimprovement is under way based on advanced small cells, cloud RadioAccess Networks (RANs), ultra-dense networks, device-to-device (D2D)communication, wireless backhaul, moving network, cooperativecommunication, Coordinated Multi-Points (CoMP), reception-endinterference cancellation and the like.

In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and slidingwindow superposition coding (SWSC) as an advanced coding modulation(ACM), and filter bank multi carrier (FBMC), non-orthogonal multipleaccess (NOMA), and sparse code multiple access (SCMA) as an advancedaccess technology have been developed.

In a 5G wireless communication system, clock synchronization betweennodes in the system is required for normal use of the system.

In a 5G communication system, network elements involve different typessuch as a user equipment (UE), an access node as a next generation nodeB (gNB), an access and mobility management function entity (AMF), asession management function entity (SMF) and a data plane functionentity, that is user plane function (UPF). Among them, the AMF, the SMFand the UPF belong to the core network elements.

In an Evolved Packet System (EPS) communication system, network elementsinvolve different types such as a UE, an access node (eNB), a mobilitymanagement entity (MME), a serving gateway (SGW) and a packet datanetwork gateway (PGW). Among them, the MME, the SGW and the PGW belongto the core network elements.

The UE may perform handover in a same communication system or betweendifferent communication systems. For example, the UE may performhandover between access nodes of a 5G communication system, that is,Intra-system handover. The UE may also perform handover between anaccess node of a 5G communication system and an access node of an EPScommunication system, that is, Inter-system handover.

FIG. 1 is a schematic diagram of a system architecture when a UEperforms handover.

The UE performs handover from a source access node (i.e., anaccess node1 connected to a core network 1) to a target access node (i.e., anaccess node 2 connected to a core network 2).

FIG. 2 is a schematic diagram that a UE establishes wireless connectionswith two access nodes at the same time.

When the UE is in the dual connectivity state, it means that the UEestablishes a wireless connection with one access node whileestablishing a wireless connection with the other access node. Oneaccess node is a Master Node. The Master Node is connected to the UEthrough a control plane indicated by a solid line and a user planeindicated by a broken line. The other access node is a Secondary Node(SN). The SN may be connected to the UE through the user plane. The twoaccess nodes may be connected to core network of a same communicationsystem, for example, the two access nodes may both be gNBs connectedwith a 5G core network. The two access nodes may also be connected tocore networks of different communication systems, for example, the twoaccess nodes may be a gNB connected with the core network of a5Gcommunication system and an eNB connected with the core network of anEPScommunication system, respectively.

SUMMARY

In view of the above one or more problems, the present inventionprovides a method for supporting handover in a mobile communicationsystem.

According to an embodiment of the present disclosure, there is provideda method for a handover of a UE, comprising: sending by a source basestation a first message to a core network element connected with thesource base station, the first message carrying UE identificationinformation for identifying the UE.

Optionally, the first message carries secondary base stationidentification information for identifying a secondary base station.

Optionally, the first message carries a source base station identifierfor identifying the source base station and/or a source cell identifierfor identifying a source cell and/or a measurement result of the UE.

Optionally, the first message is a handover request message of basestation-core network interface application protocol signaling.

Optionally, the method further comprises: receiving by the source basestation an eighth message from the core network element connected withthe source base station, the eighth message carrying a field forindicating whether the context of the UE that already exists on asecondary base station is to be kept after the handover.

Optionally, the method further comprises: receiving by the source basestation an eighth message from the core network element connected withthe source base station, the eighth message carrying the UEidentification information for identifying the UE and/or a secondarybase station identifier for identifying a secondary base station and/ora target base station identifier for identifying a target base station.

Optionally, the eighth message is a handover command message of basestation-core network interface application protocol signaling.

Optionally, the field for indicating whether the context of the UE thatalready exists on the secondary base station is to be kept after thehandover is a UE Context Kept Indicator field.

Optionally, the UE identification information is a UE identifierassigned by a secondary node to the UE.

Optionally, the UE identifier is an SgNB UE X2AP (X2 interfaceapplication protocol) ID or an S-NG-RAN node UE XnAP (Xn interfaceapplication protocol) ID.

Optionally, when the UE identification information is a cell radionetwork temporary identifier (C-RNTI) assigned by a secondary node tothe UE, the first message further carries a primary secondary cellidentifier of the UE at the secondary node and/or secondary base stationidentification information.

Optionally, the carrying is carrying directly by the message, orcarrying by a subfield carried by a Source to Target TransparentContainer field carried by the message.

Optionally, the subfield is a Source NG-RAN Node to Target NG-RAN NodeTransparent Container field, or a Source eNB to Target eNB TransparentContainer field.

Optionally, the carrying is carrying directly by the message, orcarrying by a subfield carried by a Target to Source TransparentContainer field carried by the message.

Optionally, the subfield is a Target NG-RAN Node to Source NG-RAN NodeTransparent Container field, or a Target eNB to Source eNB TransparentContainer field.

According to an embodiment of the present disclosure, there is providedan apparatus for a handover of a UE, the apparatus performing the abovemethod.

According to an embodiment of the present disclosure, there is provideda computer device for a user equipment (UE), comprising a processor anda memory storing thereon instructions, which when executed by theprocessor, performing the above method.

According to an embodiment of the present disclosure, there is provideda method for a handover of a UE, comprising: receiving by a target basestation a third message from a core network element connected with thetarget base station, the third message carrying UE identificationinformation for identifying the UE.

Optionally, the third message carries secondary base stationidentification information for identifying a secondary base station.

Optionally, the third message carries a source base station identifierfor identifying the source base station and/or a source cell identifierfor identifying a source cell and/or a measurement result of the UE.

Optionally, the third message is a handover request message of basestation-core network interface application protocol signaling.

Optionally, the method further comprises: sending by the target basestation a fourth message to the secondary base station, the fourthmessage carrying the UE identification information and/or a field forindicating a trigger scenario for the current secondary node additionpreparation process; and receiving by the target base station a fifthmessage from the secondary base station.

Optionally, the method further comprises: sending by the target basestation a fourth message to the source base station, the fourth messagecarrying the UE identification information and/or a field for indicatingthe source cell identifier of the source cell; and receiving by thetarget base station a fifth message from the source base station, thefifth message carrying the UE identification information.

Optionally, the fourth message is a secondary node addition requestmessage SGNB ADDITION REQUEST or S-NODE ADDITION REQUEST of inter-basestation interface application protocol signaling.

Optionally, the fifth message is a secondary node addition requestacknowledge message SGNB ADDITION REQUEST ACKNOWLEDGE or S-NODE ADDITIONREQUEST ACKNOWLEDGE of inter-base station interface application protocolsignaling.

Optionally, the field for indicating the trigger scenario for thecurrent secondary node addition preparation process is a secondary basestation addition trigger indication field, of inter-base stationinterface application protocol signaling, SGNB Addition TriggerIndication, and the value of the SGNB Addition Trigger Indication fieldis one of SN change, inter-eNB HO, intra-eNB HO, inter-NGRAN HO,intra-NGRAN HO, eNB-NGRAN HO and NGRAN-eNB HO.

Optionally, the field for indicating the trigger scenario for thecurrent secondary node addition preparation process is a secondary basestation addition trigger indication field, of inter-base stationinterface application protocol signaling, S-NODE Addition TriggerIndication, and the value of the S-NODE Addition Trigger Indicationfield is one of SN change, inter-eNB HO, intra-eNB HO, inter-NGRAN HO,intra-NGRAN HO, eNB-NGRAN HO and NGRAN-eNB HO.

Optionally, the method further comprises: sending by the target basestation a sixth message to a core network element connected to thetarget base station, the sixth message carrying a field for indicatingwhether the context of the UE that already exists on the secondary basestation is to be kept after the handover.

Optionally, the method further comprises: sending by the target basestation a sixth message to a core network element connected to thetarget base station, the sixth message carrying the UE identificationinformation and/or a secondary base station identifier for identifyingthe secondary base station and/or a target base station identifier foridentifying a target base station.

Optionally, the sixth message is a handover request acknowledge messageof base station-core network interface application protocol signaling.

Optionally, the field for indicating whether the context of the UE thatalready exists on the secondary base station is to be kept after thehandover is a UE Context Kept Indicator field.

Optionally, the UE identification information is a UE identifierassigned to the UE by a secondary node.

Optionally, the UE identifier is an SgNB UE X2AP ID or an S-NG-RAN nodeUE XnAP ID.

Optionally, when the UE identification information is a cell RNTIassigned by a secondary node to the UE, the third message furthercarries a primary secondary cell identifier of the UE at the secondarynode and/or secondary base station identification information.

Optionally, the carrying may be carrying directly by the message, orcarrying by a subfield carried by a Source to Target TransparentContainer field carried by the message.

Optionally, the subfield is a Source NG-RAN Node to Target NG-RAN NodeTransparent Container field, or a Source eNB to Target eNB TransparentContainer field.

Optionally, the carrying may be carrying directly by the message, orcarrying by a subfield carried by a Target to Source TransparentContainer field carried by the message.

Optionally, the subfield is a Target NG-RAN Node to Source NG-RAN NodeTransparent Container field, or a Target eNB to Source eNB TransparentContainer field.

According to an embodiment of the present disclosure, there is providedan apparatus for a handover of a UE, the apparatus performing the methodas described above.

According to an embodiment of the present disclosure, there is provideda computer device for a User Equipment (UE), comprising a processor anda memory storing thereon instructions, which when executed by theprocessor, performing the method as described above.

According to an embodiment of the present disclosure, there is provideda method for a handover of a UE, comprising: receiving by a secondarybase station a fourth message from a first master base station, thefourth message carrying UE identification information for identifyingthe UE and/or a field for indicating a trigger scenario for the currentsecondary node addition preparation process; and sending by thesecondary base station a fifth message to the first master base station.

Optionally, the fourth message is a secondary node addition requestmessage SGNB ADDITION REQUEST or S-NODE ADDITION REQUEST of inter-basestation interface application protocol signaling.

Optionally, the fifth message is a secondary node addition requestacknowledge message SGNB ADDITION REQUEST ACKNOWLEDGE or S-NODE ADDITIONREQUEST ACKNOWLEDGE of inter-base station interface application protocolsignaling.

Optionally, the field for indicating the trigger scenario for thecurrent secondary node addition preparation process is a secondary basestation addition trigger indication field, of inter-base stationinterface application protocol signaling, SGNB Addition TriggerIndication, and the value of the SGNB Addition Trigger Indication fieldis one of SN change, inter-eNB HO, intra-eNB HO, inter-NGRAN HO,intra-NGRAN HO, eNB-NGRAN HO and NGRAN-eNB HO.

Optionally, the field for indicating the trigger scenario for thecurrent secondary node addition preparation process is a secondary basestation addition trigger indication field, of inter-base stationinterface application protocol signaling, S-NODE Addition TriggerIndication, and the value of the S-NODE Addition Trigger Indicationfield is one of SN change, inter-eNB HO, intra-eNB HO, inter-NGRAN HO,intra-NGRAN HO, eNB-NGRAN HO and NGRAN-eNB HO.

Optionally, the UE identifier is an SgNB UE X2AP ID or an S-NG-RAN nodeUE XnAP ID.

Optionally, when the UE identification information is a cell RNTIassigned by a secondary node to the UE, the fourth message furthercarries a primary secondary cell identifier of the UE at the secondarynode and/or secondary base station identification information.

According to an embodiment of the present disclosure, there is providedan apparatus for a handover of a UE, the apparatus performing the methodas described above.

According to an embodiment of the present disclosure, there is provideda computer device for a user equipment (UE), comprising a processor anda memory storing thereon instructions, which when executed by theprocessor, performing the method as described above.

Before undertaking the DETAILED DESCRIPTION below, it may beadvantageous to set forth definitions of certain words and phrases usedthroughout this patent document: the terms “include” and “comprise,” aswell as derivatives thereof, mean inclusion without limitation; the term“or,” is inclusive, meaning and/or; the phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean toinclude, be included within, interconnect with, contain, be containedwithin, connect to or with, couple to or with, be communicable with,cooperate with, interleave, juxtapose, be proximate to, be bound to orwith, have, have a property of, or the like; and the term “controller”means any device, system or part thereof that controls at least oneoperation, such a device may be implemented in hardware, firmware orsoftware, or some combination of at least two of the same. It should benoted that the functionality associated with any particular controllermay be centralized or distributed, whether locally or remotely.

Moreover, various functions described below can be implemented orsupported by one or more computer programs, each of which is formed fromcomputer readable program code and embodied in a computer readablemedium. The terms “application” and “program” refer to one or morecomputer programs, software components, sets of instructions,procedures, functions, objects, classes, instances, related data, or aportion thereof adapted for implementation in a suitable computerreadable program code. The phrase “computer readable program code”includes any type of computer code, including source code, object code,and executable code. The phrase “computer readable medium” includes anytype of medium capable of being accessed by a computer, such as readonly memory (ROM), random access memory (RAM), a hard disk drive, acompact disc (CD), a digital video disc (DVD), or any other type ofmemory. A “non-transitory” computer readable medium excludes wired,wireless, optical, or other communication links that transporttransitory electrical or other signals. A non-transitory computerreadable medium includes media where data can be permanently stored andmedia where data can be stored and later overwritten, such as arewritable optical disc or an erasable memory device.

Definitions for certain words and phrases are provided throughout thispatent document, those of ordinary skill in the art should understandthat in many, if not most instances, such definitions apply to prior, aswell as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects, features and advantages of the presentdisclosure will become clearer and easier to understand through thefollowing description of the embodiments in conjunction with theaccompanying drawings, in which:

FIG. 1 shows a schematic diagram of a system architecture when a UEperforms handover;

FIG. 2 shows a schematic diagram of a UE in a dual connectivity state;

FIG. 3 shows a handover method;

FIG. 4 shows a specific example of applying the handover method shown inFIG. 3 to an intra-system handover scenario of a 5G communicationsystem;

FIG. 5 shows a handover method;

FIG. 6 shows a specific example of applying the handover method shown inFIG. 5 to an inter-system handover scenario from an EPS to a 5Gcommunication system;

FIG. 7 shows a handover method;

FIG. 8 shows a specific example of applying the handover method shown inFIG. 7 to an intra-system handover scenario of a 5G communicationsystem;

FIG. 9 shows a handover method;

FIG. 10 shows a specific example of applying the handover method shownin FIG. 9 to an intra-system handover scenario of an EPS communicationsystem;

FIG. 11 shows a specific example of applying the handover method shownin FIG. 9 to an inter-system handover scenario from an EPS to a 5Gcommunication system;

FIG. 12 shows a specific example of applying the handover method shownin FIG. 9 to an inter-system handover scenario from a 5G to an EPScommunication system;

FIG. 13 shows a specific example of applying the handover method shownin FIG. 9 to an intra-system handover scenario of a 5G communicationsystem;

FIG. 14 shows a specific example of applying the handover method shownin FIG. 5 to an inter-system handover scenario from a 5G to an EPScommunication system;

FIG. 15 shows a configuration of a network entity for next generationnode B (gNB) or evolved node B (eNB) in a communication system; and

FIG. 16 illustrates a configuration of a network node in a communicationsystem.

DETAILED DESCRIPTION

FIGS. 1 through 16 , discussed below, and the various embodiments usedto describe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged system or device

The present application provides a method for supporting handover in amobile communication network. In order to make the purpose, technicalsolution and advantages of the present application clearer, the presentapplication is described in further detail below with reference toaccompanying drawings and by way of examples.

The expressions such as “first”, “second” and “third” in thisspecification are only for distinguishing purposes, and are notrestrictive definitions.

In the following embodiments, a communication architecture in which a UEis connected to a core network element through an access node is shown.In the embodiments, the access node takes a gNB and an eNB as examples;and the core network element takes an AMF and an MME that providemobility management functions as examples.

In the following embodiments, the following interface protocols areinvolved: X2 Application Protocol (X2AP), Xn Application Protocol(XnAP), NG Application Protocol (NGAP) and S1 Application Protocol(S1AP). It should be noted that, although embodiments of the presentdisclosure are described by taking the horizontal interfaces between twobase stations being X2 and Xn as an example, the method in the presentinvention is also applicable to a case where it is other interface thatbetween the two base stations. Although embodiments of the presentinvention is described by taking the interfaces between the base stationand the core network being NG and S1 as an example, the method in thepresent invention is also applicable to a case where it is otherinterface that between the base station and the core network. That is tosay, in this specification, X2AP and XnAP are instances of inter-basestation interface application protocols, and NGAP and S1AP are instancesof base station-core network interface application protocols.

FIG. 3 is a schematic diagram of a first embodiment. The firstembodiment describes a handover method.

In the first embodiment, the handover method includes the followingsteps:

Step 301: A first node sends a first message to a third node, and thefirst message carries UE identification information.

Step 302: The third node sends a third message to a second node, and thethird message carries the UE identification information in the firstmessage.

FIG. 4 is a schematic diagram of a second embodiment. The secondembodiment is one specific example of applying the handover method inthe first embodiment to an intra-system handover scenario of a 5Gcommunication system.

In the second embodiment, before the 5G intra-system handover isperformed, the UE is in a dual connectivity state and connected to themaster node gNB 1 and the secondary node gNB 0 at the same time; afterthe 5G intra-system handover is performed, the UE is only connected togNB 0. It can be seen that, in the second embodiment, gNB 1 is a sourcenode, gNB 0 is a target node, and the target node is the secondary nodebefore the handover. The source node gNB 1 and the target node gNB 0 areboth connected to the same core network element AMF.

The source node gNB 1 may correspond to the first node in the firstembodiment, the target node gNB 0 may correspond to the second node inthe first embodiment, and the AMF may correspond to the third node inthe first embodiment.

In the above intra-system handover scenario of the 5G communicationsystem, the handover method includes the following steps:

Step 401: The source node gNB 1 sends a first message to the AMF. Thefirst message may be a HANDOVER REQUIRED message. The HANDOVER REQUIREDmessage is NGAP HANDOVER REQUIRED message in the present embodiment. TheHANDOVER REQUIRED message carries UE identification information.

Specifically, the HANDOVER REQUIRED message carries a Source to TargetTransparent Container field which may carry a Source NG-RAN Node toTarget NG-RAN Node Transparent Container field. The Source NG-RAN Nodeto Target NG-RAN Node Transparent Container field may carry the UEidentification information. Alternatively, the HANDOVER REQUIRED messagemay directly include an UE identification information.

Specifically, the UE identification information may be a UE identifierS-NG-RAN node UE XnAP ID assigned by the secondary node gNB 0 to the UEon the interface Xn. Alternatively, when the UE identificationinformation is a Cell Radio Network Temporary Identity-value (C-RNTI)assigned by the secondary node gNB 0 to the UE, the HANDOVER REQUIREDmessage further carries a Primary Secondary Cell ID (PScell ID) of theUE at the secondary node gNB 0 or the identification information of thesecondary node gNB 0.

Step 402: The AMF sends a third message to the target node gNB 0, andthe third message may be a HANDOVER REQUEST message. In the presentembodiment, the HANDOVER REQUEST message may be a NGAP HANDOVER REQUESTmessage, and the HANDOVER REQUEST message carries the UE identificationinformation in the HANDOVER REQUIRED message.

Specifically, the AMF transparently forwards the content of the Sourceto Target Transparent Container field it receives to the target node gNB0. Alternatively, if the UE identification information is directlycarried by the HANDOVER REQUIRED message in step 401, the HANDOVERREQUEST message should also directly carry the UE identificationinformation.

In the above step, when the UE identification information is the C-RNTI,the message carrying the UE identification information also carries thePScell ID of the UE at the secondary node gNB 0 or the identificationinformation of the secondary node gNB 0.

The above scheme may be advantageous. Specifically, for the downlinkdata of the UE that has been transmitted to the target node gNB 0 buthas not been transmitted to the UE before the handover is completed,since the target node gNB 0 is used as a secondary node before thehandover, the target node gNB 0 may find the context of the UE that hasbeen established on the target node gNB 0 according to the UEidentification information. When the UE identification information isthe C-RNTI, the target base station finds the context of the UE at thegNB 0 according to the received PScell ID of the UE at the secondarynode gNB 0 and/or the secondary node identification information of thegNB 0 and the UE identifier C-RNTI. The target node gNB 0 does not needto perform data forwarding before and after handover as in the existingmechanism.

Step 403: The target node gNB 0 sends a sixth message to the AMF. Thesixth message may be a HANDOVER REQUEST ACKNOWLEDGE message. TheHANDOVER REQUEST ACKNOWLEDGE message is NGAP HANDOVER REQUESTACKNOWLEDGE in the present embodiment.

Step 404: The AMF sends an eighth message to the source node gNB 1. Theeighth message may be a HANDOVER COMMAND message. The HANDOVER COMMANDmessage is NGAP HANDOVER COMMAND message in the present embodiment.

FIG. 5 is a schematic diagram of a third embodiment. The thirdembodiment describes a handover method.

In the third embodiment, the handover method includes the followingsteps:

Step 501: A first node sends a first message to a third node, and thefirst message carries UE identification information.

Step 502: The third node sends a second message to a fourth node, andthe second message carries the UE identification information in thefirst message.

Step 503: The fourth node sends a third message to a second node, andthe third message carries the UE identification information in thesecond message.

FIG. 6 is a schematic diagram of a fourth embodiment. The fourthembodiment is one specific example of applying the handover method inthe third embodiment to an inter-system handover scenario from an EPS toa 5G communication system.

In the fourth embodiment, before the inter-system handover is performed,the UE is in a dual connectivity (DC) state, and is connected to themaster node eNB 1 and the secondary node gNB 0 at the same time; afterthe inter-system handover is performed, the UE is only connected to thegNB 0. Hereinafter the dual connectivity state corresponds to an evolvedUMTS Terrestrial Radio Access Network (E-UTRAN)-new radio (NR)-DC(EN-DC). The UMTS is referred as Universal Mobile TelecommunicationSystem. It can be seen that, in the fourth embodiment, the eNB 1 is asource node, the gNB 0 is a target node, and the target node is asecondary node before the handover. The source node eNB 1 is connectedto the MME, and the target node gNB 0 is connected to the AMF.

The source node eNB 1 may correspond to the first node in the thirdembodiment, the target node gNB 0 may correspond to the second node inthe third embodiment, the MME may correspond to the third node in thethird embodiment, and the AMF may correspond to the fourth node in thethird embodiment.

In the above inter-system handover scenario from the EPS to the 5Gcommunication system, the handover method includes the following steps:

Step 601: The source node eNB 1 sends a first message to the MME. Thefirst message may be a HANDOVER REQUIRED message. The HANDOVER REQUIREDmessage isS1AP HANDOVER REQUIRED message in the present embodiment. TheHANDOVER REQUIRED message carries UE identification information and/orsecondary base station identification information.

Specifically, the HANDOVER REQUIRED message carries a Source to TargetTransparent Container field. When the target base station is a NG-RANnode, the Source to Target Transparent Container field may carry aSource NG-RAN Node to Target NG-RAN Node Transparent Container. TheSource NG-RAN Node to Target NG-RAN Node Transparent Container carriesthe UE identification information and/or the secondary base stationidentification information. Alternatively, the HANDOVER REQUIRED messagemay directly carry the UE identification information and/or thesecondary base station identification information.

Specifically, the UE identification information may be a UE identifierSgNB UE X2AP ID assigned by the secondary node gNB 0 to the UE over X2interface. Alternatively, the UE identification information may be anidentifier C-RNTI assigned by the secondary node gNB 0 to the UE. Whenthe UE identification information is the C-RNTI, the HANDOVER REQUIREDmessage further needs to include a PScell ID of UE at the secondary nodegNB 0 and/or secondary node identification information of the gNB 0.

Step 602: The MME sends a second message to the AMF. The second messagemay be a FORWARD RELOCATION REQUEST message. The FORWARD RELOCATIONREQUEST message is GPRS Tunneling Protocol (GTP) FORWARD RELOCATIONREQUEST message in the present embodiment. The FORWARD RELOCATIONREQUEST message carries the UE identification information and/or thesecondary base station identification information received in theHANDOVER REQUIRED message.

Specifically, the MME transparently forwards the content of the Sourceto Target Transparent Container field it receives to the AMF.Alternatively, in step 601, if the UE identification information and/orthe secondary base station identification information is directlycarried by the HANDOVER REQUIRED message, the GTP control plane protocolsignaling should also directly carry the UE identification informationand/or the secondary base station identification information.

Step 603: The AMF sends a third message to the target node gNB 0. Thethird message may be a HANDOVER REQUEST message. The HANDOVER REQUESTmessage is NGAP HANDOVER REQUEST message in the present embodiment. TheHANDOVER REQUEST message carries the UE identification informationand/or the secondary base station identification information in theHANDOVER REQUIRED message.

Specifically, the AMF transparently forwards the content of the Sourceto Target Transparent Container field it receives to the target node gNB0. Alternatively, in step 602, if the GTP control plane protocolsignaling directly carries the UE identification information and/or thesecondary base station identification information, the HANDOVER REQUESTmessage should also directly carry the UE identification informationand/or the secondary base station identification information.

In the above step, when the UE identification information is the C-RNTI,the message carrying the UE identification information also carries thePScell ID of the UE at the secondary node gNB 0 or the identificationinformation of the secondary node gNB 0.

The above scheme may be advantageous. Specifically, for the downlinkdata of the UE that has been transmitted to the target node gNB 0 buthas not been transmitted to the UE before the handover is completed,since the target node gNB 0 is used as a secondary node before thehandover, the target node gNB 0 may find the context of the UE that hasbeen established on the target node gNB 0 according to the UEidentification information and/or the secondary base stationidentification information, and the target node gNB 0 does not need toperform data forwarding before and after handover as in the existingmechanism. The target node gNB 0 can find the context of the UE that hasbeen established on the target node gNB 0 according to the UEidentification information and/or the secondary base stationidentification information, so as to know the bearer that has beenconfigured on the secondary base station before handover (for example, abearer terminated at the secondary node or a Secondary Cell Group (SCG)bearer). That is, the bearer is referred as an SN terminated bearer. Forthe bearer that has been configured on the secondary base station beforethe handover (for example, the bearer terminated at the secondary nodeor the SCG bearer), the data forwarding is performed in a node (i.e. thebase station) internal way, without forwarding data from the source basestation to the target base station as in the existing handovermechanism. When the UE identifier is the C-RNTI, the target base stationfinds the context of the UE at the gNB 0 according to the receivedPScell ID of the UE at the secondary node gNB 0 and/or the secondarynode identification information of the gNB 0 and the UE identifierC-RNTI.

If the gNB 0 supports separate control plane and user planearchitecture, the gNB 0 contains gNB centralized unit control plane unit(gNB-CU-CP) and gNB centralized unit user plane unit (gNB-CU-UP). ThegNB0-CU-CP requests the gNB0-CU-UP to allocate tunnel informationcorresponding to each evolved radio access bearer E-RAB. The tunnelinformation contains the transport layer address and the tunnelidentifier. The gNB0-CU-UP allocates tunnel information for dataforwarding to each requested E-RAB and sends it to the gNB0-CU-CP. Forthe bearer(s) terminated at the gNB 0 at the source side, the gNB0-CU-CPdoes not need to request gNB0-CU-UP to allocate tunnel information forthe E-RAB(s). The gNB0-CU-CP can find the UE context according to thereceived UE identification information and/or secondary base stationidentification information. The gNB0-CU-CP knows the bearer(s)terminated at the gNB0-CU-UP at the source side according to the UEcontext. The identification of the gNB0-CU-CP is the same as thesecondary base station identification of gNB 0.

Step 604: The target node gNB 0 sends a sixth message to the AMF. Thesixth message may be a HANDOVER REQUEST ACKNOWLEDGE message. TheHANDOVER REQUEST ACKNOWLEDGE message is NGAP HANDOVER REQUESTACKNOWLEDGE message in the present embodiment. For a bearer thatperforms data forwarding in a node (i.e. the base station) internal wayor a bearer that has been configured on the secondary base stationbefore the handover, the target node gNB 0 does not need to include thetransport layer address and tunnelidentifier of the bearer for dataforwarding in the HANDOVER REQUEST ACKNOWLEDGE message. The target basestation gNB 0 sends the allocated tunnel information corresponding toeach E-RAB to the AMF.

Step 605: The AMF sends a seventh message to the MME. The seventhmessage may be a FORWARD RELOCATION RESPONSE message. The FORWARDRELOCATION RESPONSE message is GTP FORWARD RELOCATION RESPONSE messagein the present embodiment.

Step 606: The MME sends an eighth message to the source node eNB 1. Theeighth message may be a HANDOVER COMMAND message. The HANDOVER COMMANDmessage is S1AP HANDOVER COMMAND message in the present embodiment.

The method can simplify the data forwarding process in the handoverprocess. The above technical scheme is described in a scenario where thesecondary base station serving the UE before the handover and the targetbase station are logically the same entity in the fourth embodiment.However, the above technical scheme is not limited thereto. In addition,the above technical scheme is also applicable to a scenario where thesecondary base station serving the UE before the handover and the targetbase station are co-located nodes. Compared with other technicalschemes, the above technical schemes can all simplify the processingprocedure of the target base station by sending a UE identifier and/or asecondary base station identifier.

FIG. 7 is a schematic diagram of a fifth embodiment. The fifthembodiment describes a handover method.

In a fifth embodiment, the handover method includes the following steps:

Step 701: A first node sends a first message to a third node, the firstmessage carries UE identification information and secondary nodeidentification information which is the identification information of afifth node.

Step 702: The third node sends a third message to a second node, and thethird message carries the UE identification information and thesecondary node identification information in the first message.

Step 703: The second node sends a fourth message to the fifth node, thefourth message carries the UE identification information in the thirdmessage and the information indicating that a secondary node is added.

Step 704: The fifth node sends a fifth message to the second node, andconfirms that the fifth node may continue to serves as a secondary nodeafter the handover.

Step 705: The second node sends a sixth message to the third node, andthe sixth message carries information indicating that the secondary noderemains unchanged before and after the handover.

Step 706: The third node sends an eighth message to the first node, andthe eighth message carries the information indicating that the secondarynode remains unchanged before and after the handover in the sixthmessage.

FIG. 8 is a schematic diagram of a sixth embodiment. The sixthembodiment is one specific example of applying the handover method inthe fifth embodiment to an intra-system handover scenario of a 5Gcommunication system.

In the sixth embodiment, before the intra-system handover is performed,the UE is in a dual connectivity state and connected to the master nodegNB 1 and the secondary node gNB 0 at the same time; after theintra-system handover is performed, the UE is still in the dualconnectivity state and connected to the master node gNB 2 and thesecondary node gNB 0 that remains unchanged before and after thehandover at the same time. It can be seen that, in the sixth embodiment,the gNB 1 is a source node, the gNB 2 is a target node, and thesecondary node before and after the handover remain unchanged as the gNB0. Wherein, the source node gNB 1 and the target node gNB 2 are bothconnected to the AMF.

The source node gNB 1 may correspond to the first node in the fifthembodiment, the target node gNB 2 may correspond to the second node inthe fifth embodiment, the secondary node gNB 0 may correspond to thefifth node in the fifth embodiment, and the AMF may correspond to thethird node in the fifth embodiment.

In the above intra-system handover scenario of the 5G communicationsystem, the handover method includes the following steps:

Step 801: The source node gNB 1 sends a first message to the AMF. Thefirst message may be a HANDOVER REQUIRED message. The HANDOVER REQUIREDmessage is NGAP HANDOVER REQUIRED message in the present embodiment. TheHANDOVER REQUIRED message carries UE identification information andidentification information of the secondary node gNB 0.

Specifically, the HANDOVER REQUIRED message may carry a Source to TargetTransparent Container field which may carry a Source NG-RAN Node toTarget NG-RAN Node Transparent Container field. The Source NG-RAN Nodeto Target NG-RAN Node Transparent Container field carries the UEidentification information and the identification information of thesecondary node gNB 0. Alternatively, the HANDOVER REQUIRED message maydirectly include information elements for indicating the UEidentification information and the identification information of thesecondary node gNB 0, so as to directly carry the UE identificationinformation and the identification information of the secondary node gNB0.

Specifically, the UE identification information may be a UE identifierS-NG-RAN node UE XnAP ID assigned by the secondary node gNB 0 to the UEon the interface Xn. Alternatively, the UE identification informationmay be an identifier C-RNTI assigned by the secondary node gNB 0 to theUE. When the UE identification information is the C-RNTI, the HANDOVERREQUIRED message further needs to include a PScell ID of the UE at thesecondary node gNB 0 and/or the secondary node identificationinformation of the gNB 0.

Step 802: The AMF sends a third message to the target node gNB 2. Thethird message may be a HANDOVER REQUEST message. The HANDOVER REQUESTmessage is NGAP HANDOVER REQUEST message in the present embodiment. TheHANDOVER REQUEST message carries the UE identification information andthe identification information of the secondary node gNB 0 in theHANDOVER REQUIRED message.

Specifically, the AMF may transparently forward the content of theSource to Target Transparent Container field it receives to the targetnode gNB 2. Alternatively, in step 801, if the HANDOVER REQUIRED messagedirectly carries the UE identification information and theidentification information of the secondary node gNB 0, the HANDOVERREQUEST message should also directly carry the UE identificationinformation and the identification information of the secondary node gNB0.

The above scheme may be advantageous. Specifically, the target node gNB2 will determine whether the secondary node gNB 0 is able to remainunchanged as a secondary node after the handover according to thereceived identification information of the secondary node gNB 0.Therefore, the secondary node identification information makes itpossible for the secondary node gNB 0 before the handover to remainunchanged after the handover is completed, providing the possibility ofavoiding unnecessary forwarding.

Step 803: The target node gNB 2 sends a fourth message to the secondarynode gNB 0. The fourth message may be a secondary node addition requestmessage which may be anXnAPS-NODE ADDITION REQUEST message in thepresent embodiment. The S-NODE ADDITION REQUEST message includes the UEidentification information and/or an S-NODE Addition Trigger Indicationfield. The S-NODE Addition Trigger Indication field indicates that thetrigger scenario for the current secondary node addition preparationprocess is an inter-NGRAN node handover, that is, the S-NODE AdditionTrigger Indication field takes a value of inter-NGRAN HO.

In the above step, when the UE identification information is the C-RNTI,the above message carrying the UE identification information alsocarries the PScell ID of the UE at the secondary node gNB 0 or theidentification information of the secondary node gNB 0.

The above scheme may be advantageous. Specifically, the inter-NGRAN nodehandover is explicitly defined as a trigger scenario for the secondarynode addition preparation process.

Similarly, the S-NODE Addition Trigger Indication field can also take avalue of intra-NGRAN HO, so that the intra-NGRAN node handover can alsobe explicitly defined as a trigger scenario for the secondary nodeaddition preparation process.

Step 804: The secondary node gNB 0 sends a fifth message to the targetnode gNB 2. The fifth message may be a secondary node addition requestacknowledge message. The secondary node addition request acknowledgemessage may be anXnAPS-NODE ADDITION REQUEST ACKNOWLEDGE message in thepresent embodiment. The S-NODE ADDITION REQUEST ACKNOWLEDGE messagecarries an RRC Config Indication field.

The above scheme may be advantageous. Specifically, for the downlinkdata of the UE that has been transmitted to the secondary node gNB 0 buthas not been transmitted to the UE before the handover is completed,since the secondary node gNB 0 is used as a secondary node before thehandover, the secondary node gNB 0 may find the context of the UE thathas been established on the secondary node gNB 0 according to the UEidentification information, and the secondary node gNB 0 does not needto perform data forwarding before and after handover as in the existingmechanism. When the UE identifier is the C-RNTI, the secondary basestation finds the context of the UE at the gNB 0 according to the PScellID of the UE at the secondary node gNB 0 and/or the secondary nodeidentification information of the gNB 0 and the UE identifier C-RNTI.

Step 805: The target node gNB 2 sends a sixth message to the AMF. Thesixth message may be a HANDOVER REQUEST ACKNOWLEDGE message. TheHANDOVER REQUEST ACKNOWLEDGE message is NGAP HANDOVER REQUESTACKNOWLEDGE message in the present embodiment. The HANDOVER REQUESTACKNOWLEDGE message may carry a Target To Source Transparent Containerfield which may carry a Target NG-RAN Node to Source NG-RAN NodeTransparent Container field. The Target NG-RAN Node to Source NG-RANNode Transparent Container field may carry a UE Context Kept Indicatorfield to indicate whether the context of the UE already existing on thesecondary node gNB 0 is to be kept after the handover is ended.Alternatively, the HANDOVER REQUEST ACKNOWLEDGE message may directlyinclude a UE Context Kept Indicator field to directly carry informationabout whether the context of the UE already existing on the secondarynode gNB 0 is to be kept after the handover is ended.

Step 806: The AMF sends an eighth message to the source node gNB 1. Theeighth message may be a HANDOVER COMMAND message. The HANDOVER COMMANDmessage is NGAP HANDOVER COMMAND message in the present embodiment. TheHANDOVER COMMAND message carries a UE Context Kept Indicator field.

Specifically, the AMF may transparently forward the content of theTarget To Source Transparent Container field it receives to the sourcenode gNB 1. Alternatively, in step 805, if the HANDOVER REQUESTACKNOWLEDGE message directly carries the UE Context Kept Indicatorfield, the HANDOVER COMMAND message should also directly carry the UEContext Kept Indicator field.

Step 807: The source node gNB 1 sends a ninth message to the secondarynode gNB 0. The ninth message may be a secondary node release requestmessage. The secondary node release request message may be anXnAPS-NODERELEASE REQUEST message in the present embodiment. The S-NODE RELEASEREQUEST message includes a UE Context Kept Indicator field.

The above scheme may be advantageous. Specifically, the secondary nodegNB 0 will determine, according to the UE Context Kept Indicator field,whether the context of the UE already existing thereon is to be keptafter the handover is ended. Therefore, the data about the UE at thesecondary node 0 can be prevented from being deleted erroneously orunnecessarily.

Step 808: The secondary node gNB 0 sends a tenth message to the sourcenode gNB 1. The tenth message may be a secondary node release requestacknowledge message. The secondary node release request acknowledgemessage may be anXnAPS-NODE RELEASE REQUEST ACKNOWLEDGE message in thepresent embodiment.

FIG. 9 is a schematic diagram of a seventh embodiment. The seventhembodiment describes a handover method.

In the seventh embodiment, the handover method includes the followingsteps:

Step 901: A first node sends a first message to a third node. The firstmessage carries UE identification information and secondary nodeidentification information which is the identification information ofthe fifth node.

Step 902: The third node sends a second message to a fourth node, andthe second message carries the UE identification information and thesecondary node identification information in the first message.

Step 903: The fourth node sends a third message to a second node, andthe third message carries the UE identification information and thesecondary node identification information in the second message.

Step 904: The second node sends a fourth message to the fifth node, andthe fourth message carries the UE identification information in thethird message and scenario information indicating that a secondary nodeis currently added.

Step 905: The fifth node sends a fifth message to the second node, andconfirms that the fifth node can continue to be a secondary node afterthe handover.

Step 906: The second node sends a sixth message to the fourth node, andthe sixth message carries information indicating that the secondary noderemains unchanged before and after the handover.

Step 907: The fourth node sends a seventh message to the third node, andthe seventh message carries the information indicating that thesecondary node remains unchanged before and after the handover in thesixth message.

Step 908: The third node sends an eighth message to the first node, andthe eighth message carries the information indicating that the secondarynode remains unchanged before and after the handover in the seventhmessage.

FIG. 10 is a schematic diagram of an eighth embodiment. The eighthembodiment is one specific example of applying the handover method inthe seventh embodiment to an intra-system handover scenario of an EPScommunication system.

In the eighth embodiment, before the intra-system handover is performed,the UE is in a dual connectivity state and is connected to the masternode eNB 1 and the secondary node gNB 0 at the same time; after theintra-system handover based on the interface S1 is performed by the UE,the UE is still in the dual connectivity state and is connected to themaster node eNB 2 and the secondary node gNB 0 that remains unchangedbefore and after the handover at the same time. It can be seen that, inthe eighth embodiment, eNB 1 is a source node, eNB 2 is a target node,and the secondary node before and after the handover remains unchangedas gNB 0. Wherein, the source node eNB 1 is connected to the source MME,and the target node eNB 2 is connected to the target MME.

The source node eNB 1 may correspond to the first node in the seventhembodiment, the target node eNB 2 may correspond to the second node inthe seventh embodiment, the source MME may correspond to the thirdnodein the seventh embodiment, the target MME may correspond to the fourthnode in the seventh embodiment, and the secondary node gNB 0 maycorrespond to the fifth node in the seventh embodiment.

In the above intra-system handover scenario of the EPS communicationsystem, the handover method includes the following steps:

Step 1001: The source node eNB sends a first message to the source MME.The first message may be a HANDOVER REQUIRED message. The HANDOVERREQUIRED message is S1AP HANDOVER REQUIRED message in the presentembodiment. The HANDOVER REQUIRED message carries UE identificationinformation and the identification information of the secondary node gNB0.

Specifically, the HANDOVER REQUIRED message carries a Source to TargetTransparent Container field which may carry a Source eNB to Target eNBTransparent Container field. The Source eNB to Target eNB TransparentContainer field carries the UE identification information and theidentification information of the secondary node gNB 0. Alternatively,the HANDOVER REQUIRED message may directly include information elementsfor indicating the UE identification information and the identificationinformation of the secondary node gNB 0, so as to directly carry the UEidentification information and the identification information of thesecondary node gNB 0.

Specifically, the UE identification information may be a UE identifierSgNB UE X2AP ID assigned by the secondary node gNB 0 to the UE over X2interface. Alternatively, the UE identification information may be anidentifier C-RNTI assigned by the secondary node gNB 0 to the UE. Whenthe UE identification information is the C-RNTI, the HANDOVER REQUIREDmessage further needs to include a PScell ID of the UE at the secondarynode gNB 0 or the secondary node identification information of the gNB0.

Step 1002: The source MME sends a second message to the target MME. Thesecond message may be a FORWARD RELOCATION REQUEST message. The FORWARDRELOCATION REQUEST message is GTP FORWARD RELOCATION REQUEST message inthe present embodiment. The FORWARD RELOCATION REQUEST message carriesthe UE identification information and the identification information ofthe secondary node gNB 0 in the HANDOVER REQUIRED message.

Specifically, the source MME transparently forwards the content of theSource to Target Transparent Container field it receives to the targetMME. Alternatively, in step 1001, if the UE identification informationand the identification information of the secondary node gNB 0 aredirectly carried by the HANDOVER REQUIRED message, the FORWARDRELOCATION REQUEST message of GTP control plane protocol signalingshould also directly carry the UE identification information and theidentification information of the secondary node gNB 0.

Step 1003: The target MME sends a third message to the target node eNB2. The third message may be a HANDOVER REQUEST message. The HANDOVERREQUEST message is S1AP HANDOVER REQUEST message in the presentembodiment. The HANDOVER REQUEST message carries the UE identificationinformation and the identification information of the secondary node gNB0 in the HANDOVER REQUIRED message.

Specifically, the target MME transparently forwards the content of theSource to Target Transparent Container field it receives to the targetnode eNB 2. Alternatively, in step 1002, if the UE identificationinformation and the identification information of the secondary node gNB0 are directly carried by the FORWARD RELOCATION REQUEST message, theHANDOVER REQUEST message should also directly carry The UEidentification information and the identification information of thesecondary node gNB 0.

The above scheme may be advantageous. Specifically, the target node eNB2 will determine whether the secondary node gNB 0 is able to remainunchanged as a secondary node after the handover according to thereceived identification information of the secondary node gNB 0.Therefore, the secondary node identification information makes itpossible for the secondary node gNB 0 before the handover to bemaintained after the handover is completed, providing the possibility ofavoiding unnecessary forwarding.

Step 1004: The target node eNB 2 sends a fourth message to the secondarynode gNB 0. The fourth message may be a secondary node addition requestmessage which includes the UE identification information and/or asecondary node addition trigger indication. The secondary node additionrequest message may be anX2AP SGNB ADDITION REQUEST message in thepresent embodiment. The SGNB ADDITION REQUEST message includes the UEidentification information and/or an SGNB Addition Trigger Indicationfield. The SGNB Addition Trigger Indication field indicates that thetrigger scenario for the current secondary node addition preparationprocess is an inter-eNB handover, that is, the SGNB Addition TriggerIndication field takes a value of inter-eNB HO.

In the above step, when the UE identification information is the C-RNTI,the message carrying the UE identification information also carries thePScell ID of the UE at the secondary node gNB 0 or the identificationinformation of the secondary node gNB 0.

The above scheme may be advantageous. Specifically, the inter-eNBhandover is explicitly defined as a secondary node addition preparationprocess trigger scenario.

Step 1005: The secondary node gNB 0 sends a fifth message to the targetnode eNB 2. The fifth message may be a secondary node addition requestacknowledge message which may be anX2AP SGNB ADDITION REQUESTACKNOWLEDGE message. The SGNB ADDITION REQUEST ACKNOWLEDGE messagecarries an RRC Config Indication field.

The above scheme may be advantageous. Specifically, for the downlinkdata of the UE that has been transmitted to the secondary node gNB 0 buthas not been transmitted to the UE before the handover is completed,since the secondary node gNB 0 is used as a secondary node before thehandover, the secondary node gNB 0 may find the context of the UE thathas been established on the secondary node gNB 0 according to the UEidentification information, and the secondary node gNB 0 does not needto perform data forwarding before and after handover as in the existingmechanism. When the UE identifier is the C-RNTI, the secondary basestation finds the context of the UE at the gNB 0 according to the PScellID of the UE at the secondary node gNB 0 and/or the secondary nodeidentification information of the gNB 0 and the UE identifier C-RNTI.

Step 1006: The target node eNB sends a sixth message to the target MME.The sixth message may be a HANDOVER REQUEST ACKNOWLEDGE message. TheHANDOVER REQUEST ACKNOWLEDGE message is S1AP HANDOVER REQUESTACKNOWLEDGE message. The HANDOVER REQUEST ACKNOWLEDGE message may carrya Target To Source Transparent Container field which may carry a TargeteNB to Source eNB Transparent Container field. The Target eNB to SourceeNB Transparent Container field may carry a UE Context Kept Indicatorfield to indicate whether the context of the UE already existing on thesecondary node gNB 0 is to be kept after the handover is ended.Alternatively, the HANDOVER REQUEST ACKNOWLEDGE message may directlyinclude a UE Context Kept Indicator field to directly carry informationabout whether the context of the UE already existing on the secondarynode gNB 0 is to be kept after the handover is ended.

Step 1007: The target MME sends a seventh message to the source MME. Theseventh message may be a FORWARD RELOCATION RESPONSE message. TheFORWARD RELOCATION RESPONSE message is GTP FORWARD RELOCATION RESPONSEmessage. The FORWARD RELOCATION RESPONSE message carries the UE ContextKept Indicator in the HANDOVER REQUEST ACKNOWLEDGE message.

Specifically, the target MME may transparently forward the content ofthe Target To Source Transparent Container field it receives to thesource MME. Alternatively, in step 1006, if the HANDOVER REQUESTACKNOWLEDGE message directly carries the UE Context Kept Indicatorfield, the FORWARD RELOCATION RESPONSE message of GTP control planeprotocol signaling should also directly carry the UE Context KeptIndicator field.

Step 1008: The source MME sends an eighth message to the source nodeeNB 1. The eighth message may be a HANDOVER COMMAND message. TheHANDOVER COMMAND message is S1AP HANDOVER COMMAND message. The HANDOVERCOMMAND message carries a UE Context Kept Indicator field.

Specifically, the source MME may transparently forward the content ofthe Target To Source Transparent Container field it receives to thesource node eNB1. Alternatively, in step 1007, if the FORWARD RELOCATIONRESPONSE message directly carries the UE Context Kept Indicator field,the HANDOVER COMMAND message should also directly carry the UE ContextKept Indicator field.

Step 1009: The source node eNB 1 sends a ninth message to the secondarynode gNB 0. The ninth message may be a secondary node release requestmessage which may be anX2AP SGNB RELEASE REQUEST message. The SGNBRELEASE REQUEST message includes a UE Context Kept Indicator field.

The above scheme may be advantageous. Specifically, the secondary nodegNB 0 will determine, according to the UE Context Kept Indicator field,whether the context of the UE already existing thereon is to be keptafter the handover is ended. Therefore, the data about the UE at thesecondary node 0 can be prevented from being deleted erroneously orunnecessarily.

Step 1010: The secondary node gNB 0 sends a tenth message to the sourcenode eNB 1. The tenth message may be a secondary node release requestacknowledge message which may be anX2AP SGNB RELEASE REQUEST ACKNOWLEDGEmessage.

FIG. 11 is a schematic diagram of a ninth embodiment. The ninthembodiment is one specific example of applying the handover method inthe seventh embodiment to a handover scenario from an EPS communicationsystem to a 5G communication system.

In the ninth embodiment, before the inter-system handover is performed,the UE is in a dual connectivity state and is simultaneously connectedto the master node eNB 1 and the secondary node gNB 0; after the UEperforms a handover from the EPS system to the 5G system, the UE isstill in a dual connectivity state and is connected to the master nodegNB 2 and the secondary node gNB 0 that remains unchanged before andafter the handover at the same time. It can be seen that, in the ninthembodiment, eNB 1 is a source node, gNB 2 is a target node, and thesecondary node before and after the handover remains unchanged as gNB 0.The source node eNB 1 is connected to the MME, and the target node gNB 2is connected to the AMF.

The source node eNB 1 may correspond to the first node in the seventhembodiment, the target node gNB 2 may correspond to the second node inthe seventh embodiment, the MME may correspond to the third node in theseventh embodiment, the AMF may correspond to the fourth node in theseventh embodiment, and the secondary node gNB 0 may correspond to thefifth node in the seventh embodiment.

In the above handover scenario from the EPS communication system to the5G communication system, the handover method includes the followingsteps:

Step 1101: The source node eNB sends a first message to the MME. Thefirst message may be a HANDOVER REQUIRED message. The HANDOVER REQUIREDmessage is S1AP HANDOVER REQUIRED message. The HANDOVER REQUIRED messagecarries UE identification information and identification information ofthe secondary node gNB 0.

Specifically, the HANDOVER REQUIRED message carries a Source to TargetTransparent Container field which may carry a Source NG-RAN Node toTarget NG-RAN Node Transparent Container field. The Source NG-RAN Nodeto Target NG-RAN Node Transparent Container field carries the UEidentification information and the identification information of thesecondary node gNB 0. Alternatively, the HANDOVER REQUIRED message maydirectly include information elements for indicating the UEidentification information and the identification information of thesecondary node gNB 0, so as to directly carry the UE identificationinformation and the identification information of the secondary node gNB0.

Specifically, the UE identification information may be a UE identifierSgNB UE X2AP ID assigned by the secondary node gNB 0 to the UE over X2interface. Alternatively, the UE identification information may be anidentifier C-RNTI assigned by the secondary node gNB 0 to the UE. Whenthe UE identification information is the C-RNTI, the HANDOVER REQUIREDmessage further needs to include a PScell ID of the UE at the secondarynode gNB 0 and/or the secondary node identification information of thegNB 0.

Step 1102: the MME sends a second message to the AMF. The second messagemay be a FORWARD RELOCATION REQUEST message. The FORWARD RELOCATIONREQUEST message is GTP FORWARD RELOCATION REQUEST message. The FORWARDRELOCATION REQUEST message carries the UE identification information andthe identification information of the secondary node gNB 0 in theHANDOVER REQUIRED message.

Specifically, the MME transparently forwards the content of the Sourceto Target Transparent Container field it receives to the AMF.Alternatively, in step 1101, if the UE identification information andthe identification information of the secondary node gNB 0 are directlycarried by the HANDOVER REQUIRED message, the FORWARD RELOCATION REQUESTmessage of GTP control plane protocol signaling should also directlycarry the UE identification information and the identificationinformation of the secondary node gNB 0.

Step 1103: the AMF sends a third message to the target node gNB 2. Thethird message may be a HANDOVER REQUEST message. The HANDOVER REQUESTmessage is NGAP HANDOVER REQUEST message. The HANDOVER REQUEST messagecarries the UE identification information and the identificationinformation of the secondary node gNB 0 in the HANDOVER REQUIREDmessage.

Specifically, the AMF transparently forwards the content of the Sourceto Target Transparent Container field it receives to the target node gNB2. Alternatively, in step 1102, if the UE identification information andthe identification information of the secondary node gNB 0 are directlycarried by the FORWARD RELOCATION REQUEST message, the HANDOVER REQUESTmessage of NGAP signaling should also directly carry the UEidentification information and the identification information of thesecondary node gNB 0.

The above scheme may be advantageous. Specifically, the target node gNB2 will determine whether the secondary node gNB 0 is able to remainunchanged as a secondary node after the handover according to thereceived identification information of the secondary node gNB 0.Therefore, the identification information of the secondary node makes itpossible for the secondary node gNB 0 before the handover to bemaintained after the handover is completed, providing the possibility ofavoiding unnecessary forwarding.

Step 1104: The target node gNB 2 sends a fourth message to the secondarynode gNB 0. The fourth message may be a secondary node addition requestmessage which includes the UE identification information and/or asecondary node addition trigger indication. The secondary node additionrequest message may be anXnAPS-NODE ADDITION REQUEST message. The S-NODEADDITION REQUEST message includes the UE identification informationand/or an S-NODE Addition Trigger Indication field. The S-NODE AdditionTrigger Indication field indicates that the trigger scenario for thecurrent secondary node addition preparation process is an eNB-NGRANhandover, that is, the S-NODE Addition Trigger Indication field takes avalue of eNB-NGRAN HO.

In the above step, when the UE identification information is the C-RNTI,the message carrying the UE identification information also carries thePScell ID of the UE at the secondary node gNB 0 or the identificationinformation of the secondary node gNB 0.

The above scheme may be advantageous. Specifically, the eNB-NGRANhandover is explicitly defined as a trigger scenario for the secondarynode addition preparation process.

Step 1105: The secondary node gNB 0 sends a fifth message to the targetnode gNB 2. The fifth message may be a secondary node addition requestacknowledge message which may be anXnAPS-NODE ADDITION REQUESTACKNOWLEDGE message. The S-NODE ADDITION REQUEST ACKNOWLEDGE messagecarries an RRC Config Indication field.

The above scheme may be advantageous. Specifically, for the downlinkdata of the UE that has been transmitted to the secondary node gNB 0 buthas not been transmitted to the UE before the handover is completed,since the secondary node gNB 0 is used as a secondary node before thehandover, the secondary node gNB 0 may find the context of the UE thathas been established on the secondary node gNB 0 according to the UEidentification information, and the secondary node gNB 0 does not needto perform data forwarding before and after handover as in the existingmechanism. When the UE identifier is the C-RNTI, the secondary node basestation finds the context of the UE at the gNB 0 according to the PScellID of the UE at the secondary node gNB 0 and/or the secondary nodeidentification information of the gNB 0 and the UE identifier C-RNTI.

Step 1106: The target node gNB 2 sends a sixth message to the AMF. Thesixth message may be a HANDOVER REQUEST ACKNOWLEDGE message. TheHANDOVER REQUEST ACKNOWLEDGE message is NGAP HANDOVER REQUESTACKNOWLEDGE message. The HANDOVER REQUEST ACKNOWLEDGE message may carrya Target To Source Transparent Container field which may carry a TargetNG-RAN Node to Source NG-RAN Node Transparent Container field. TheTarget NG-RAN Node to Source NG-RAN Node Transparent Container field maycarry a UE Context Kept Indicator field to indicate whether the contextof the UE already existing on the secondary node gNB 0 is to be keptafter the handover is ended. Alternatively, the HANDOVER REQUESTACKNOWLEDGE message may directly include a UE Context Kept Indicatorfield to directly carry information about whether the context of the UEalready existing on the secondary node gNB 0 is to be kept after thehandover is ended.

Step 1107: The AMF sends a seventh message to the MME. The seventhmessage may be a FORWARD RELOCATION REQUEST message. The FORWARDRELOCATION RESPONSE message is GTP FORWARD RELOCATION REQUEST message.

The FORWARD RELOCATION RESPONSE message carries the UE Context KeptIndicator in the HANDOVER REQUEST ACKNOWLEDGE message.

Specifically, the AMF transparently forwards the content of the TargetTo Source Transparent Container field it receives to the MME.Alternatively, in step 1106, if the HANDOVER REQUEST ACKNOWLEDGE messagedirectly carries the UE Context Kept Indicator field, the FORWARDRELOCATION RESPONSE message of GTP control plane protocol signalingshould also directly carry the UE Context Kept Indicator field.

Step 1108: The MME sends an eighth message to the source node eNB 1. Theeighth message may be a HANDOVER COMMAND message. The HANDOVER COMMANDmessage is S1AP HANDOVER COMMAND message. The HANDOVER COMMAND messagecarries a UE Context Kept Indicator field.

Specifically, the MME may transparently forward the content of theTarget To Source Transparent Container sub-segment it receives to thesource node eNB1. Alternatively, in step 1107, if the FORWARD RELOCATIONRESPONSE message directly carries the UE Context Kept Indicator field,the HANDOVER COMMAND message should also directly carry the field UEContext Kept Indicator.

Step 1109: The source node eNB 1 sends a ninth message to the secondarynode gNB 0. The ninth message may be a secondary node release requestmessage which may be anX2AP SGNB RELEASE REQUEST message. The SGNBRELEASE REQUEST message includes a UE Context Kept Indicator field.

The above scheme may be advantageous. Specifically, the secondary nodegNB 0 will determine, according to the UE Context Kept Indicator field,whether the context of the UE already existing thereon is to be keptafter the handover is ended. Therefore, the data about the UE at thesecondary node 0 can be prevented from being deleted erroneously orunnecessarily.

Step 1110: The secondary node gNB 0 sends a tenth message to the sourcenode eNB 1. The tenth message may be a secondary node release requestacknowledge message which may be anX2AP SGNB RELEASE REQUEST ACKNOWLEDGEmessage.

FIG. 12 is a schematic diagram of a tenth embodiment. The tenthembodiment is one specific example of applying the handover method inthe seventh embodiment to a handover scenario between a 5G communicationsystem and an EPS communication system.

In the tenth embodiment, before the inter-system handover is performed,the UE is in a dual connectivity state and is connected to the masternode gNB 1 and the secondary node gNB 0 at the same time; after the UEperforms a handover from the 5G system to the EPS system, the UE isstill in a dual connectivity state and is connected to the master nodeeNB 2 and the secondary node gNB 0 that remains unchanged before andafter the handover at the same time. It can be seen that, in the tenthembodiment, gNB 1 is a source node, eNB 2 is a target node, and thesecondary node before and after the handover remains unchanged as gNB 0.The source node gNB 1 is connected to the AMF, and the target node gNB 2is connected to the MME.

The source node gNB 1 may correspond to the first node in the seventhembodiment, the target node eNB 2 may correspond to the second node inthe seventh embodiment, the AMF may correspond to the third node in theseventh node, the MME may correspond to the fourth node in the seventhembodiment, and the secondary node gNB 0 may correspond to the fifthnode in the seventh embodiment.

In the above handover scenario from the 5G communication system to theEPS communication system, the handover method includes the followingsteps:

Step 1201: The source node gNB 1 sends a first message to the AMF. Thefirst message may be a HANDOVER REQUIRED message. The HANDOVER REQUIREDmessage is NGAP HANDOVER REQUIRED message. The HANDOVER REQUIRED messagecarries UE identification information and identification information ofthe secondary node gNB 0.

Specifically, the HANDOVER REQUIRED message carries a Source to TargetTransparent Container field which may carry a Source eNB to Target eNBTransparent Container field. The Source eNB to Target eNB TransparentContainer field carries the UE identification information and theidentification information of the secondary node gNB 0. Alternatively,the HANDOVER REQUIRED message may directly include information elementsfor indicating the UE identification information and the identificationinformation of the secondary node gNB 0, so as to directly carry the UEidentification information and the identification information of thesecondary node gNB 0.

Specifically, the UE identification information may be an identifierS-NG-RAN node UE XnAP ID assigned by the secondary node gNB 0 to the UEon the interface Xn. Alternatively, the UE identification informationmay be an identifier C-RNTI assigned by the secondary node gNB 0 to theUE. When the UE identification information is the C-RNTI, the HANDOVERREQUIRED message further needs to include a PScell ID of the secondarynode gNB 0 and/or the secondary node identification information of thegNB 0.

Step 1202: The AMF sends a second message to the MME. The second messagemay be a FORWARD RELOCATION REQUEST message. The FORWARD RELOCATIONREQUEST message is GTP FORWARD RELOCATION REQUEST message. The FORWARDRELOCATION REQUEST message carries the UE identification information andthe identification information of the secondary node gNB 0 in theHANDOVER REQUIRED message.

Specifically, the AMF transparently forwards the content of the Sourceto Target Transparent Container field it receives to the MIME.Alternatively, in step 1201, if the UE identification information andthe identification information of the secondary node gNB 0 are directlycarried by the HANDOVER REQUIRED message, the FORWARD RELOCATION REQUESTmessage of GTP control plane protocol signaling should also directlycarry the UE identification information and the identificationinformation of the secondary node gNB 0.

Step 1203: The MME sends a third message to the target node eNB 2. Thethird message may be a HANDOVER REQUEST message. The HANDOVER REQUESTmessage is S1APHANDOVER REQUEST message. The HANDOVER REQUEST messagecarries the UE identification information and the identificationinformation of the secondary node gNB 0 in the HANDOVER REQUIREDmessage.

Specifically, the MME transparently forwards the content of the Sourceto Target Transparent Container field it receives to the target node eNB2. Alternatively, in step 1202, if the UE identification information andthe identification information of the secondary node gNB 0 are directlycarried by the FORWARD RELOCATION REQUEST message, the HANDOVER REQUESTmessage of S1AP signaling should also directly carry the UEidentification information and the identification information of thesecondary node gNB 0.

The above scheme may be advantageous. Specifically, the target node eNB2 determines whether the secondary node gNB 0 is able to remainunchanged as a secondary node after the handover according to thereceived identification information of the secondary node gNB 0.Therefore, the secondary node identification information makes itpossible for the secondary node gNB 0 before the handover to bemaintained after the handover is completed, providing the possibility ofavoiding unnecessary forwarding.

Step 1204: The target node eNB 2 sends a fourth message to the secondarynode gNB 0. The fourth message may be a secondary node addition requestmessage which includes the UE identification information and/or asecondary node addition trigger indication. The secondary node additionrequest message may be anX2AP SGNB ADDITION REQUEST message. The SGNBADDITION REQUEST message includes the UE identification informationand/or an SGNB Addition Trigger Indication field. The SGNB AdditionTrigger Indication field indicates that the trigger scenario for thecurrent secondary node addition preparation process is an NGRAN-eNBhandover, that is, the SGNB Addition Trigger Indication field takes avalue of NGRAN-eNB HO.

In the above step, when the UE identification information is the C-RNTI,the message carrying the UE identification information also carries thePScell ID of the UE at the secondary node gNB 0 or the identificationinformation of the secondary node gNB 0.

The above scheme may be advantageous. Specifically, the NGRAN-eNBhandover is explicitly defined as a trigger scenario for the secondarynode addition preparation process.

Step 1205: The secondary node gNB 0 sends a fifth message to the targetnode eNB 2. The fifth message may be a secondary node addition requestacknowledge message which may be anX2AP SGNB ADDITION REQUESTACKNOWLEDGE message. The SGNB ADDITION REQUEST ACKNOWLEDGE messagecarries an RRC Config Indication field.

The above scheme may be advantageous. Specifically, for the downlinkdata of the UE that has been transmitted to the secondary node gNB 0 buthas not been transmitted to the UE before the handover is completed,since the secondary node gNB 0 is used as a secondary node before thehandover, the secondary node gNB 0 may find the context of the UE thathas been established on the secondary node gNB 0 according to the UEidentification information, and the secondary node gNB 0 does not needto perform data forwarding before and after handover as in the existingmechanism. When the UE identifier is the C-RNTI, the secondary basestation finds the context of the UE at the gNB 0 according to the PScellID of the UE at the secondary node gNB 0 and/or the secondary nodeidentification information of the gNB 0 and the UE identifier C-RNTI.

Step 1206: The target node eNB 2 sends a sixth message to the MME. Thesixth message may be a HANDOVER REQUEST ACKNOWLEDGE message. TheHANDOVER REQUEST ACKNOWLEDGE message is S1AP HANDOVER REQUESTACKNOWLEDGE message. The HANDOVER REQUEST ACKNOWLEDGE message may carrya Target To Source Transparent Container field which may carry a TargeteNB to Source eNB Transparent Container field. The Target eNB to SourceeNB Transparent Container field may carry a UE Context Kept Indicatorfield to indicate whether the context of the UE already existing on thesecondary node gNB 0 is to be kept after the handover is ended.Alternatively, the HANDOVER REQUEST ACKNOWLEDGE message may directlyinclude a UE Context Kept Indicator field to directly carry informationabout whether the context of the UE already existing on the secondarynode gNB 0 is to be kept after the handover is ended.

Step 1207: The MME sends a seventh message to the AMF. The seventhmessage may be a FORWARD RELOCATION RESPONSE message. The FORWARDRELOCATION RESPONSE message is GTP FORWARD RELOCATION RESPONSE message.The FORWARD RELOCATION RESPONSE message carries the UE Context KeptIndicator in the HANDOVER REQUEST ACKNOWLEDGE message.

Specifically, the MME transparently forwards the content of the TargetTo Source Transparent Container field it receives to the AMF.Alternatively, in step 1206, if the HANDOVER REQUEST ACKNOWLEDGE messagedirectly carries the UE Context Kept Indicator field, the FORWARDRELOCATION RESPONSE message of GTP control plane protocol signalingshould also directly carry the UE Context Kept Indicator field.

Step 1208: The AMF sends an eighth message to the source node gNB 1. Theeighth message may be a HANDOVER COMMAND message. The HANDOVER COMMANDmessage is NGAP HANDOVER COMMAND message. The HANDOVER COMMAND messagecarries the UE Context Kept Indicator field.

Specifically, the AMF may transparently forward the content of theTarget To Source Transparent Container field it receives to the sourcenode gNB 1. Alternatively, in step 1207, if the FORWARD RELOCATIONRESPONSE message directly carries the UE Context Kept Indicator field,the HANDOVER COMMAND message should also directly carry the UE ContextKept Indicator field.

Step 1209: The source node gNB 1 sends a ninth message to the secondarynode gNB 0. The ninth message may be a secondary node release requestmessage which may be anXnAPS-NODE RELEASE REQUEST message. The S-NODERELEASE REQUEST message includes a UE Context Kept Indicator field.

The above scheme may be advantageous. Specifically, the secondary nodegNB 0 will determine, according to the UE Context Kept Indicator field,whether the context of the UE already existing thereon is to be keptafter the handover is ended. Therefore, the data about the UE at thesecondary node 0 can be prevented from being deleted erroneously orunnecessarily.

Step 1210: The secondary node gNB 0 sends a tenth message to the sourcenode gNB 1. The tenth message may be a secondary node release requestacknowledge message which may be anXnAPS-NODE RELEASE REQUESTACKNOWLEDGE message.

FIG. 13 is a schematic diagram of an eleventh embodiment. The eleventhembodiment is one specific example of applying the handover method inthe seventh embodiment to an intra-system handover scenario of a 5Gcommunication system.

In the eleventh embodiment, before the intra-system handover isperformed, the UE is in a dual connectivity state and is connected tothe master node gNB 1 and the secondary node gNB 0 at the same time;after the UE performs the intra-system handover of the 5G system, the UEis still in a dual connectivity state and is connected to the masternode gNB 2 and the secondary node gNB 0 that remains unchanged beforeand after the handover at the same time. It can be seen that, in theeleventh embodiment, gNB 1 is a source node, gNB 2 is a target node, andthe secondary node before and after the handover remains unchanged asgNB 0. The source node gNB 1 is connected to the source AMF, and thetarget node gNB 2 is connected to the target AMF.

The source node gNB 1 may correspond to the first node in the seventhembodiment, the target node gNB 2 may correspond to the second node inthe seventh embodiment, the source AMF may correspond to the third nodein the seventh embodiment, the target AMF may correspond to the fourthnode in the seventh embodiment, and the secondary node gNB 0 maycorrespond to the fifth node in the seventh embodiment.

In the above intra-system handover scenario of the 5G communicationsystem, the handover method includes the following steps:

Step 1301: The source node gNB 1 sends a first message to the sourceAMF. The first message may be a HANDOVER REQUIRED message. The HANDOVERREQUIRED message is NGAP HANDOVER REQUIRED message. The HANDOVERREQUIRED message carries UE identification information andidentification information of the secondary node gNB 0.

Specifically, the HANDOVER REQUIRED message carries a Source to TargetTransparent Container field which may carry a Source NG-RAN Node toTarget NG-RAN Node Transparent Container field. The Source NG-RAN Nodeto The Target NG-RAN Node Transparent Container field carries the UEidentification information and the identification information of thesecondary node gNB 0. Alternatively, the HANDOVER REQUIRED message maydirectly include information elements for indicating the UEidentification information and the identification information of thesecondary node gNB 0, so as to directly carry the UE identificationinformation and the identification information of the secondary node gNB0.

Specifically, the UE identification information may be a UE identifierS-NG-RAN node UE XnAP ID assigned by the secondary node gNB 0 to the UEon the interface Xn. Alternatively, the UE identification informationmay be an identifier C-RNTI assigned by the secondary node gNB 0 to theUE. When the UE identifier is the C-RNTI, the HANDOVER REQUIRED messagefurther needs to include a PScell ID of the UE at the secondary node gNB0 and/or the secondary node identification information of the gNB 0.

Step 1302: The source AMF sends a second message to the target AMF. Thesecond message may be a Namf_Communication_CreateUEContext Requestmessage. The Namf_Communication_CreateUEContext Request message is AMFNamf_Communication_CreateUEContext Request message which carries the UEidentification information and the identification information of thesecondary node gNB 0 in the HANDOVER REQUIRED message.

Specifically, the source AMF transparently forwards the content of theSource to Target Transparent Container field it receives to the targetAMF. Alternatively, in step 1301, if the UE identification informationand the identification information of the secondary node gNB 0 aredirectly carried by the HANDOVER REQUIRED message, theNamf_Communication_CreateUEContext Request message of AMF interfacesignaling should also directly carry the UE identification informationand the identification information of the secondary node gNB 0.

Step 1303: The source AMF sends a third message to the target node gNB2. The third message may be a HANDOVER REQUEST message. The HANDOVERREQUEST message is NGAP HANDOVER REQUEST message. The HANDOVER REQUESTmessage carries the UE identification information and the identificationinformation of the secondary node gNB 0 in the HANDOVER REQUIREDmessage.

Specifically, the AMF transparently forwards the content of the Sourceto Target Transparent Container field it receives to the target node gNB2. Alternatively, in step 1302, if the UE identification information andthe identification information of the secondary node gNB 0 are directlycarried by the Namf_Communication_CreateUEContext Request message of AMFinterface signaling, the HANDOVER REQUEST message of NGAP signalingshould also directly carry the UE identification information and theidentification information of the secondary node gNB 0.

The above scheme may be advantageous. Specifically, the target node gNB2 will determine whether the secondary node gNB 0 is able to remainunchanged as a secondary node after the handover according to thereceived identification information of the secondary node gNB 0.Therefore, the secondary node identification information makes itpossible for the secondary node gNB 0 before the handover to bemaintained after the handover is completed, providing the possibility ofavoiding unnecessary forwarding.

Step 1304: The target node gNB 2 sends a fourth message to the secondarynode gNB 0. The fourth message may be a secondary node addition requestmessage which includes the UE identification and/or a secondary nodeaddition trigger indication. The secondary node addition request messagemay be anXnAPS-NODE ADDITION REQUEST message. The S-NODE ADDITIONREQUEST message includes the UE identification information and/or anS-NODE Addition Trigger Indication field. The S-NODE Addition TriggerIndication field indicates that the trigger scenario for the currentsecondary node addition preparation process is an inter-NGRAN nodehandover, that is, the S-NODE Addition Trigger Indication field takes avalue of inter-NGRAN HO.

In the above step, when the UE identification information is the C-RNTI,the message carrying the UE identification information also carries thePScell ID of the UE at the secondary node gNB 0 or the identificationinformation of the secondary node gNB 0.

The above scheme may be advantageous. Specifically, the inter-NGRAN nodehandover is explicitly defined as a trigger scenario for the secondarynode addition preparation process.

Step 1305: The secondary node gNB 0 sends a fifth message to the targetnode gNB 2. The fifth message may be a secondary node addition requestacknowledge message which may be anXnAP S-NODE ADDITION REQUESTACKNOWLEDGE message. The S-NODE ADDITION REQUEST ACKNOWLEDGE messagecarries an RRC Config Indication field.

The above scheme may be advantageous. Specifically, for the downlinkdata of the UE that has been transmitted to the secondary node gNB 0 buthas not been transmitted to the UE before the handover is completed,since the secondary node gNB 0 is used as a secondary node before thehandover, the secondary node gNB 0 may find the context of the UE thathas been established on the secondary node gNB 0 according to the UEidentification information, and the secondary node gNB 0 does not needto perform data forwarding before and after handover as in the existingmechanism. When the UE identifier is the C-RNTI, the secondary basestation finds the context of the UE at the gNB 0 according to the PScellID of the UE at the secondary node gNB 0 and/or the secondary nodeidentification information of the gNB 0 and the UE identifier C-RNTI.

Step 1306: The target node gNB 2 sends a sixth message to the targetAMF. The sixth message may be a HANDOVER REQUEST ACKNOWLEDGE message.The HANDOVER REQUEST ACKNOWLEDGE message is NGAP HANDOVER REQUESTACKNOWLEDGE message. The HANDOVER REQUEST ACKNOWLEDGE message may carrya Target To Source Transparent Container field which may carry a TargetNG-RAN Node to Source NG-RAN Node Transparent Container field. TheTarget NG-RAN Node to Source NG-RAN Node Transparent Container field maycarry a UE Context Kept Indicator field to indicate whether the contextof the UE already existing on the secondary node gNB 0 is to be keptafter the handover is ended. Alternatively, the HANDOVER REQUESTACKNOWLEDGE message may directly include the UE Context Kept Indicatorfield to directly carry information about whether the context of the UEalready existing on the secondary node gNB 0 is to be kept after thehandover is ended.

Step 1307: The target AMF sends a seventh message to the source AMF. Theseventh message may be a Namf_Communication_CreateUEContext Responsemessage. The Namf_Communication_CreateUEContext Response message is AMFNamf_Communication_CreateUEContext Response message which carries the UEContext Kept Indicator in the HANDOVER REQUEST ACKNOWLEDGE message.

Specifically, the target AMF transparently forwards the content of theTarget To Source Transparent Container field it receives to the sourceAMF. Alternatively, in step 1306, if the HANDOVER REQUEST ACKNOWLEDGEmessage directly carries the UE Context Kept Indicator field, theNamf_Communication_CreateUEContext Response message of AMF interfacesignaling should also directly carry the UE Context Kept Indicatorfield.

Step 1308: The source AMF sends an eighth message to the source nodegNB 1. The eighth message may be a HANDOVER COMMAND message. TheHANDOVER COMMAND message is NGAP HANDOVER COMMAND message. The HANDOVERCOMMAND message carries the UE Context Kept Indicator field.

Specifically, the source AMF can transparently forward the content ofthe Target To Source Transparent Container field it receives to thesource node gNB 1. Alternatively, in step 1307, if the AMF interfacesignaling Namf_Communication_CreateUEContext Response directly carriesthe UE Context Kept Indicator field, the signaling HANDOVER COMMANDshould also directly carry the UE Context Kept Indicator field.

Step 1309: The source node gNB 1 sends a ninth message to the secondarynode gNB 0. The ninth message may be a secondary node release requestmessage which may be anXnAPS-NODE RELEASE REQUEST message. The S-NODERELEASE REQUEST message includes the UE Context Kept Indicator field.

The above scheme may be advantageous. Specifically, the secondary nodegNB 0 will determine, according to the UE Context Kept Indicator field,whether the context of the UE already existing thereon is to be keptafter the handover is ended. Therefore, the data about the UE at thesecondary node 0 can be prevented from being deleted erroneously orunnecessarily.

Step 1310: The secondary node gNB 0 sends a tenth message to the sourcenode gNB 1. The tenth message may be a secondary node release requestacknowledge message which may be anXnAP S-NODE RELEASE REQUESTACKNOWLEDGE message.

FIG. 14 is a schematic diagram of a twelfth embodiment. The twelfthembodiment is one specific example of applying the handover method inthe third embodiment to an inter-system handover scenario from a 5Gcommunication system to an EPS communication system.

In the twelfth embodiment, before the inter-system handover isperformed, the UE is only connected to the gNB 0; after the inter-systemhandover is performed, the UE is in a dual connectivity state and isconnected to the master node eNB 1 and the secondary node gNB 0 at thesame time. It can be seen that, in the twelfth embodiment, the gNB 0 isa source node, the eNB 1 is a target node, and the source node is thesecondary node after the handover. The source base station gNB 0 isconnected to the AMF, and the target base station eNB 1 is connected tothe MME.

The source node gNB 0 may correspond to the first node in the thirdembodiment, the target node eNB 1 may correspond to the second node inthe third embodiment, the AMF may correspond to the third node in thethird embodiment, and the MME may correspond to the fourth node in thethird embodiment.

In the above inter-system handover scenario from the 5G communicationsystem to the EPS system, the handover method includes the followingsteps:

Step 1401: The source node gNB 0 sends a first message to the AMF. Thefirst message may be a HANDOVER REQUIRED message. The HANDOVER REQUIREDmessage is NGAP HANDOVER REQUIRED message in this embodiment. TheHANDOVER REQUIRED message carries a source base station identifierand/or a source cell identifier and/or UE identification informationand/or a measurement result of the UE.

Specifically, the HANDOVER REQUIRED message carries a Source to TargetTransparent Container field. When the target node is an E-UTRAN basestation, the Source to Target Transparent Container field may carry aSource eNB to Target eNB Transparent Container. The Source eNB to TargeteNB Transparent Container carries the source base station identifierand/or the source cell identifier and/or the UE identificationinformation and/or the measurement result of the UE. Alternatively, theHANDOVER REQUIRED message may directly include the source base stationidentifier and/or the source cell identifier and/or the UEidentification information and/or the measurement result of the UE.Specifically, the UE identification information may be a C-RNTI assignedby the source node gNB 0 to the UE. In the case where the UE identifieris the C-RNTI, the identifier of the source cell also needs to becarried directly by the HANDOVER REQUIRED message or carried in theSource eNB to Target eNB Transparent Container field.

Step 1402: The AMF sends a second message to the MME. The second messagemay be a FORWARD RELOCATION REQUEST. The FORWARD RELOCATION REQUESTmessage is GTP FORWARD RELOCATION REQUEST message in this embodiment.The FORWARD RELOCATION REQUEST message carries the source base stationidentifier and/or the source cell identifier and/or the UEidentification information and/or the measurement result of the UE inthe HANDOVER REQUIRED message.

Specifically, the AMF transparently forwards the content of the Sourceto Target Transparent Container field it receives to the MME.Alternatively, in step 1401, if the source base station identifierand/or the source cell identifier and/or the UE identificationinformation and/or the measurement result of the UE are directly carriedby the HANDOVER REQUIRED message, the GTP The control plane protocolsignaling should also directly carry the source base station identifierand/or the source cell identifier and/or the UE identificationinformation and/or the measurement result of the UE.

Step 1403: The MME sends a third message to the target base stationeNB 1. The third message may be a HANDOVER REQUEST message. The HANDOVERREQUEST message is S1AP HANDOVER REQUEST message in this embodiment. TheHANDOVER REQUEST message carries the source base station identifierand/or the source cell identifier and/or the UE identificationinformation and/or the measurement result of the UE in the HANDOVERREQUIRED message.

Specifically, the MME transparently forwards the content of the Sourceto Target Transparent Container field it receives to the target basestation eNB1. Alternatively, in step 1402, if the GTP control planeprotocol signaling directly carries the source base station identifierand/or the source cell identifier and/or the UE identificationinformation and/or the measurement result of the UE, the HANDOVERREQUEST message should also directly carry the source base stationidentifier and/or the source cell identifier and/or the UEidentification information and/or the measurement result of the UE.

Step 1404: The targeteNB 1 decides to initiate a secondary node additionprocess to the source gNB 0. The targeteNB 1 decides to initiate an SNaddition process to the source gNB 0 according to the received UEmeasurement report and/or the source base station identifier and/or thesource cell identifier.

The targeteNB 1 sends an SN addition request message to the gNB 0. Thesecondary node addition request message includes a UE identifierassigned by the source base station to the UE and/or a source cellidentifier and/or source base station identifier. The UE identifier is aUE identifier received from the source base station gNB 0 through aHANDOVER REQUEST message. The message includes bearer information to beconfigured on the gNB 0.

The gNB 0 receives a secondary node addition request message. The gNB 0can retrieve the context of the UE according to the UE identifier and/orthe source cell identifier received in the message. For a bearerconfigured onto the gNB 0 (for example, a bearer terminating at asecondary node or an SCG bearer), the gNB 0 does not need to assign atransport layer address and a tunnel identifier for data forwarding. ThegNB 0 only needs to perform internal data forwarding.

If the gNB 0 supports separate control plane and user planearchitecture, the gNB 0 contains gNB centralized unit control plane unit(gNB-CU-CP) and gNB centralized unit user plane unit (gNB-CU-UP). ThegNB0-CU-CP requests the gNB0-CU-UP to allocate tunnel informationcorresponding to each evolved radio access bearer E-RAB for thebearer(s) terminated at the gNB0-CU-UP. The tunnel information containsthe transport layer address and the tunnel identifier. The gNB0-CU-UPallocates tunnel information for data forwarding to each requested E-RABand sends it to the gNB0-CU-CP. For the bearer(s) terminated at the eNB1at the target side, the gNB0-CU-CP does not need to request gNB0-CU-UPto allocate tunnel information for the E-RAB. The gNB0-CU-CP can findthe UE context according to the received UE identifier and/or sourcecell identifier. The gNB0-CU-CP knows the bearer(s) terminated at thegNB0-CU-UP at the target side according to the UE context. Theidentification of the gNB0-CU-CP is the same as the secondary basestation identification of gNB 0.

The gNB 0 sends an SN addition request acknowledge message to the eNB 1.The gNB 0 does not need to include the transport layer address and thetunnel identifier for data forwarding into the message. The secondarynode addition request acknowledge message includes a UE identifier overthe interface between the gNB 0 and the eNB 1 assigned by the gNB 0. TheUE identifier may be an SgNB UE X2AP ID or an S-NG-RAN node UE XnAP ID.

Step 1405: The targeteNB 1 sends a sixth message to the MME. The sixthmessage may be a HANDOVER REQUEST ACKNOWLEDGE message. The HANDOVERREQUEST ACKNOWLEDGE message is S1AP HANDOVER REQUEST ACKNOWLEDGE messagein this embodiment. For a bearer that performs data forwarding in a node(i.e. the base station) internal way or a bearer to be configured on thesource base station after the handover, the target node eNB 1 does notneed to include the transport layer address and the tunnel identifier ofthe bearer for data forwarding in the HANDOVER REQUEST ACKNOWLEDGEmessage. The HANDOVER REQUEST ACKNOWLEDGE message directly carries, orthe Target to Source Transparent Container field in the HANDOVER REQUESTACKNOWLEDGE message carries the UE identifier over the interface betweenthe gNB 0 and the eNB 1 assigned by the gNB 0, and/or the secondary basestation identifier of the gNB 0, and/or the target base stationidentifier of the eNB 1.

Step 1406: The MME sends a seventh message to the AMF. The seventhmessage may be a FORWARD RELOCATION RESPONSE message. The FORWARDRELOCATION RESPONSE message is GTP FORWARD RELOCATION RESPONSE messagein this embodiment. The FORWARD RELOCATION RESPONSE message carries theUE identifier over the interface between the gNB 0 and the eNB 1assigned by the gNB 0, and/or the secondary base station identifier ofthe gNB 0, and/or the target base station identifier of the eNB 1.

Step 1407: The AMF sends an eighth message to the source base stationgNB 0. The eighth message may be a HANDOVER COMMAND message. TheHANDOVER COMMAND message is NGAP HANDOVER COMMAND message in thisembodiment. The HANDOVER COMMAND message carries the UE identifier overthe interface between the gNB 0 and the eNB 1 assigned by the gNB 0,and/or the secondary base station identifier of the gNB 0, and/or thetarget base station identifier of the eNB 1.

The gNB 0 finds the context of the UE according to the received UEidentifier over the interface between the gNB 0 and the eNB assigned bythe gNB 0 and/or secondary base station identifier of the gNB 0 and/ortarget base station identifier of the eNB 1. For a bearer configuredonto the gNB 0 at the target base station eNB 1 (for example, a bearerterminating at a secondary node or an SCG bearer), the gNB 0 performsinternal data forwarding.

If the gNB 0 supports separate control plane and user planearchitecture, the gNB0-CU-CP receives tunnel information for dataforwarding corresponding to each E-RAB. The tunnel information containsthe transport layer address and tunnel identifier. The gNB0-CU-CP sendstunnel information corresponding to each E-RAB to the gNB0-CU-UP. Forthe bearer(s) terminated at the gNB0-CU-UP at the target side, thegNB0-CU-CP does not need to send the E-RAB tunnel information to thegNB0-CU-UP. For the bearer terminated at the target node eNB1 at thetarget side, the gNB0-CU-CP sends the E-RAB tunnel information to thegNB0-CU-UP. The gNB0-CU-CP finds the UE context according to thereceived UE identifier over the interface between the gNB 0 and eNBallocated by the gNB0-CU-CP, and/or the secondary base stationidentifier of gNB 0, and/or the target base station identifier of eNB 1.The gNB0-CU-CP knows the bearer(s) terminated at the gNB0-CU-UP at thetarget side according to the UE context. The identification of thegNB0-CU-CP is the same as the secondary base station identification ofgNB 0. For the bearer(s) terminated at the gNB0-CU-UP at the targetside, the gNB0-CU-UP performs internal data forwarding. For a bearerterminated at the eNB 1 at the target side, the gNB0-CU-UP forwards thedata to eNB 1. For the direct data forwarding, the gNB0-CU-UP sends datato the tunnel corresponding to each E-RAB. The data sent by gNB0-CU-UPto each E-RAB tunnel has no service quality assurance (Qos) flowidentification (QFI) information. The gNB0-CU-UP sends the data of eachQos flow to the corresponding E-RAB tunnel according to the mapping ofper Qos flow to a corresponding the E-RAB.

Step 1408: A subsequent handover process is performed.

The method can simplify the data forwarding process in the handoverprocess. The above technical scheme is described in a scenario where thesource base station and the secondary base station serving the UE afterthe handover are logically the same entity in the fourteenth embodiment.However, the above technical scheme is not limited thereto. In addition,the above technical scheme is also applicable to a scenario where thesecondary base station serving the UE after the handover and the sourcebase station are co-located nodes. On the one hand, the source basestation identifier and/or the source cell identifier and/or the UEidentification information and/or the measurement result of the UE aresent by the source base station to the target base station, and sent bythe target base station to the source base station as the secondary basestation, so that for the bearer configured onto the source base station(for example, a bearer terminating at a secondary node or an SCGbearer), the source base station performs internal data forwarding. Onthe other hand, the target base station may also send the UE identifierover the interface between the gNB 0 and the eNB assigned by the gNB 0and/or the secondary node identifier of the gNB 0 and/or the target nodeidentifier of the eNB 1 to the source base station gNB 0, the gNB 0finds the context of the UE according to the UE identifier and/or thesecondary node identifier of the gNB 0 and/or the target node identifierof the eNB 1 it receives, and for the bearer configured onto gNB 0 atthe target base station eNB 1 (for example, a bearer terminating at asecondary node bearer or an SCG bearer), the gNB 0 performs internaldata forwarding. This technical scheme includes the above two aspects tobe implemented in a combined or separate manner. Compared with othertechnical schemes, the above technical scheme does not need to forwarddata from the source base station to the target base station and fromthe target master base station to the target secondary base station asin the existing handover mechanism.

In summary, according to the present disclosure, the secondary nodeidentification information makes it possible for the connection with thesecondary node before the handover to be maintained after the handoveris completed, providing the possibility of avoiding unnecessaryforwarding; further, the secondary node can determines, according to therelated information, whether the context of the UE already existingthereon is to be kept after the handover is ended, thereby avoiding thatthe data about the UE is erroneously or unnecessarily deleted;furthermore, for the downlink data of the UE that has been transmittedto the secondary node but has not been transmitted to the UE before thehandover is completed, when the secondary node is used as a secondarynode before the handover, the secondary node can find the context of theUE that has been established thereon according to the UE identificationinformation, and the secondary node does not need to perform dataforwarding before and after the handover as in the existing mechanism,avoiding the waste of resources and reducing the delay of the downlinkdata; even further, trigger scenarios for the secondary node additionpreparation process that are not explicitly defined in the existingmechanism are defined.

FIG. 15 shows a configuration of a network entity for next generationnode B (gNB) or evolved node B (eNB) in a communication system.

FIG. 15 shows a configuration of a network entity in a wirelesscommunication system according to various embodiments. The configurationillustrated in FIG. 15 may be understood as a configuration of thenetwork entity. Terms such as “ . . . unit”, “ . . . device” used belowrefer to a unit for processing at least one function or operation, whichmay be implemented by hardware, software, or a combination of hardwareand software. For example, the network entity comprises a base station.The network entity may be refereed as next generation node B (gNB) orevolved node B (eNB).

Referring to FIG. 15 , the network entity includes a wirelesscommunication unit 1510, a backhaul communication unit 1520, a storageunit 1530, and a controller 1540.

The wireless communication unit 1510 performs functions for transmittingand receiving a signal via a wireless channel. For example, the wirelesscommunication unit 1510 performs a function of conversion between abaseband signal and a bitstream according to the physical layer standardof the system. For example, the wireless communication unit 1510generates complex symbols during data transmission by encoding andmodulating a transmission bitstream. In addition, the wirelesscommunication unit 1510 restores, when receiving data, a receptionbitstream through demodulation and decoding of the baseband signal.

In addition, the wireless communication unit 1510 up-converts a basebandsignal into an RF (radio-frequency) band signal and then transmits thesignal via an antenna, and down-converts an RF-band signal received viathe antenna into a baseband signal. To this end, the wirelesscommunication unit 1510 may include a transmission filter, a receptionfilter, an amplifier, a mixer, an oscillator, a DAC (digital-to-analogconvertor), and an ADC (analog-to-digital converter). In addition, thewireless communication unit 1510 may include a plurality oftransmission/reception paths. Furthermore, the wireless communicationunit 1510 may include at least one antenna array configured by aplurality of antenna elements.

With regard to hardware, the wireless communication unit 1510 may beconfigured by a digital unit and an analog unit, and the analog unit maybe configured by a plurality of sub-units according to operating power,operating frequency, and the like. The digital unit may be implementedas at least one processor (e.g., DSP (digital signal processor)). Thewireless communication unit 1510 transmits and receives a signal asdescribed above. Accordingly, all or part of the wireless communicationunit 1510 may be referred to as a “transmitter”, a “receiver”, or a“transceiver”. In addition, transmission and reception performed via awireless channel are used in the following description as a meaning ofincluding a process performed as described above by the wirelesscommunication unit 1510.

A backhaul communication unit 1520 provides an interface for performingcommunication with other nodes in a network. That is, the backhaulcommunication unit 1520 converts a bitstream transmitted from a networkentity to another node, for example, another access node, anothernetwork entity, an upper node, a core network, or the like into aphysical signal, and converts a physical signal received from anothernode into a bitstream.

The storage unit 1530 stores data, such as a basic program,applications, and configuration information, for the operation of anetwork entity. The storage unit 1530 may configured as volatile memory,nonvolatile memory, or a combination of volatile memory and nonvolatilememory. Further, the storage unit 1530 provides the stored data at therequest of the controller 1540.

The controller 1540 controls the overall operations of a network entity.For example, the controller 1540 transmits and receives a signal via thewireless communication unit 1510 or the backhaul communication unit1520. In addition, the controller 1540 records and reads data in thestorage unit 1530. The controller 1540 may perform the functions of aprotocol stack required by a communication standard. According toanother embodiment, the protocol stack may be included in the wirelesscommunication unit 1510. To this end, the controller 1540 may include atleast one processor. According to various embodiments, the controller1540 may control the network entity to perform operations according tovarious embodiments described above.

FIG. 16 illustrates a configuration of a network node in a communicationsystem. The configuration shown in FIG. 16 may be understood as aconfiguration of a device having at least one function of any corenetwork entity like AMF, SMF, UPF, or MME. Terms such as “ . . . unit”,“ . . . device” used below refer to a unit that processes at least onefunction or operation, which may be implemented by hardware or software,or a combination of hardware and software.

Referring to FIG. 16 , the network node includes a communication unit1610, a storage unit 1620, and a controller 1630.

The communication unit 1610 provides an interface for performingcommunication with other devices in a network. That is, thecommunication unit 1610 converts a bitstream transmitted from thenetwork node to another device into a physical signal, and converts aphysical signal received from another device into a bitstream. That is,the communication unit 1610 may transmit and receive signals.Accordingly, the communication unit 1610 may be referred to as a modem,a transmitter, a receiver, or a transceiver. At this time, thecommunication unit 1610 allows the network node to communicate withother devices or systems via a backhaul connection (e.g., wired backhaulor wireless backhaul) or via a network.

The storage unit 1620 stores data, such as a basic program,applications, and configuration information, for the operation of thenetwork node. The storage unit 1620 may be configured as volatilememory, nonvolatile memory, or a combination of volatile memory andnonvolatile memory. Further, the storage unit 1620 provides the storeddata at the request of the controller 1630.

The controller 1630 controls the overall operations of a networkfunction in the core network. For example, the controller 1630 transmitsand receives a signal via the communication unit 1610. In addition, thecontroller 1630 records and reads data in the storage unit 1620. To thisend, the controller 1630 may include at least one processor. Accordingto various embodiments, the controller 1630 may control a core networkentity to perform operations according to various embodiments describedabove.

According to embodiments, a method for User Equipment (UE) handover,comprising: sending by a source base station a first message to a corenetwork element connected with the source base station, the firstmessage carrying UE identification information for identifying the UE.

In some embodiments, the first message carries secondary base stationidentification information for identifying a secondary base station.

In some embodiments, the first message carries a source base stationidentifier for identifying the source base station and/or a source cellidentifier for identifying a source cell and/or a measurement result ofthe UE.

In some embodiments, the first message is a handover request message ofbase station-core network interface application protocol signaling.

In some embodiments, the method further comprises receiving by thesource base station an eighth message from the core network elementconnected with the source base station, the eighth message carrying afield for indicating whether the context of the UE that already existson a secondary base station is to be kept after the handover.

In some embodiments, the method further comprises receiving by thesource base station an eighth message from the core network elementconnected with the source base station, the eighth message carrying theUE identification information for identifying the UE and/or a secondarybase station identifier for identifying a secondary base station and/ora target base station identifier for identifying a target base station.

In some embodiments, the eighth message is a handover command message ofbase station-core network interface application protocol signaling.

In some embodiments, the field for indicating whether the context of theUE that already exists on the secondary base station is to be kept afterthe handover is a UE Context Kept Indicator field.

In some embodiments, the UE identification information is a UEidentifier assigned by a secondary node to the UE.

In some embodiments, the UE identifier is an SgNB UE X2AP ID or anS-NG-RAN node UE XnAP ID.

In some embodiments, when the UE identification information is a cellradio network temporary identifier C-RNTI assigned by a secondary nodeto the UE, the first message further carries a primary secondary cellidentifier of the UE at the secondary node and/or secondary base stationidentification information.

In some embodiments, the carrying is carrying directly by the message,or carrying by a subfield carried by a Source to Target TransparentContainer field carried by the message.

In some embodiments, the carrying is carrying directly by the message,or carrying by a subfield carried by a Target to Source TransparentContainer field carried by the message.

According to embodiments, an apparatus for User Equipment (UE) handoverperforms any one of the above methods.

According to embodiments, a computer device for a User Equipment (UE),comprising a processor and a memory storing thereon instructions, whichwhen executed by the processor, performs one of the above methods.

While embodiments of the disclosure have been described in the above, itshould be recognized that these descriptions are merely illustrative andnot restrictive. In addition, in the above, the definitions of “basestation” and “node” can be used and understood equivalently.

As will be appreciated by those skilled in the art, the presentinvention includes devices related to performing one or more of theoperations described in this application. These devices may be speciallydesigned and manufactured for the required purpose, or may include knowndevices in general-purpose computers. These devices have computerprograms stored therein that are selectively activated or reconstructed.Such computer program may be stored in a device (e.g., a computer)readable medium or in any type of medium suitable for storing electronicinstructions and coupled to a bus, respectively. The computer readablemedium includes, but not limited to, any types of disks (includingfloppy disks, hard disks, optical disks, CD-ROMs, and magneto-opticaldisks), ROM (Read-Only Memory), RAM (Random Access Memory), EPROM(Erasable Programmable Read-Only Memory), EEPROM (Electrically ErasableProgrammable Read-Only Memory), flash memory, magnetic card or opticalcard. That is, a readable medium includes any medium that stores ortransports information in a readable form by a device (e.g., acomputer).

Those skilled in the art may understand that these computer programinstructions may be provided to a general-purpose computer, aprofessional computer or a processor of other programmable dataprocessing methods to be realized, so that the scheme disclosed in thepresent invention may be performed by the computer or the processor ofother programmable data processing method.

Those skilled in the art may understand that steps, measures and schemesin various operations, methods, processes that have been discussed inthe present invention can be alternated, modified, combined or deleted.Further, other steps, measures and schemes in various operations,methods, processes that have been discussed in the present invention canalso be alternated, modified, rearranged, decomposed, combined ordeleted. Further, the prior art that have steps, measures and schemes invarious operations, methods, processes having been disclosed in thepresent invention can also be alternated, modified, rearranged,decomposed, combined or deleted.

The above described are merely preferred embodiments of the presentapplication and are not intended to limit the present application. Anymodification, equivalent replacement, improvement, combination, partialcombination, etc. made within the spirit and principle of theapplication should all be included in the protection scope of thisapplication.

Although the present disclosure has been described with variousembodiments, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

What is claimed is:
 1. A method performed by an access and mobilitymanagement function (AMF), the method comprising: receiving, from amobility management entity (MME) for an evolved node B (eNB), a messageassociated with a handover required message for an inter-system handoverof at user equipment (UE) from an evolved packet system (EPS) to 5Gsystem (5GS) with a secondary gNB (SgNB) used as a target nextgeneration node B (gNB); transmitting, to the target gNB, a handoverrequest message for the inter-system handover from the EPS to the 5GSwith the SgNB used as the target gNB; and receiving, from the targetgNB, an acknowledge of the handover request message, wherein the SgNBand the target gNB are co-located in a network entity, wherein the eNBis associated with the SgNB in a dual connectivity, wherein the handoverrequired message includes an SgNB UE X2 application protocol ID (SgNB UEX2AP ID) for identifying the UE over an X2 interface in the SgNB,wherein the handover request message includes the SgNB UE X2AP ID, andwherein the SgNB UE X2AP ID is allocated at the SgNB.
 2. The method ofclaim 1, wherein the SgNB and the target gNB corresponds to a samenetwork entity, wherein the handover required message includes a SourceNG-RAN Node to Target NG-RAN Node Transparent Container field forcarrying the SgNB UE X2 application protocol ID, and wherein thehandover request message includes a Source NG-RAN Node to Target NG-RANNode Transparent Container field for carrying the SgNB UE X2 applicationprotocol ID.
 3. The method of claim 1, further comprising: transmitting,to the MME, a message to transmit a handover command message from theMME to the eNB.
 4. A method performed by a network entity, the methodcomprising: receiving, from an access and mobility management function(AMF), a handover request message for an inter-system handover of a userequipment (UE) from an evolved packet system (EPS) to 5G system (5GS)with a secondary gNB SgNB used as a target next generation node B (gNB);and transmitting, to the AMF, an acknowledge of the handover requestmessage, wherein the SgNB and the target gNB are co-located in thenetwork entity, wherein the SgNB is associated with an evolved node B(eNB) in a dual connectivity, wherein the handover request messageincludes SgNB user equipment (UE) X2 application protocol ID (SgNB UEX2AP ID) for identifying the UE over an X2 interface in the SgNB, andwherein the SgNB UE X2AP ID is allocated at the SgNB.
 5. The method ofclaim 4, further comprising: if a bearer terminated at the SgNB isidentified, performing a data forwarding in a node-internal way for thebearer terminated at the SgNB.
 6. The method of claim 4, wherein theSgNB and the target gNB corresponds to a same network entity, andwherein the handover request message includes a Source NG-RAN Node toTarget NG-RAN Node Transparent Container field for carrying the SgNB UEX2 application protocol ID.
 7. A method performed by an evolved node B(eNB), the method comprising: transmitting, to a mobility managemententity (MME), a handover required message for an inter-system handoverof a user equipment (UE) from an evolved packet system (EPS) to 5Gsystem (5GS) with a secondary gNB (SgNB) used as a target nextgeneration node B (gNB); and receiving, from the MME, a handover commandmessage, wherein the SgNB and the target gNB are co-located in a networkentity, wherein the eNB is associated with the SgNB in a dualconnectivity, wherein the handover required message includes SgNB UE X2application protocol ID (SgNB UE X2AP ID) for identifying the UE over anX2 interface in the SgNB, and wherein the SgNB UE X2AP ID is allocatedat the SgNB.
 8. The method of claim 7, wherein the SgNB and the targetgNB corresponds to a same network entity, and wherein the handoverrequired message includes a Source NG-RAN Node to Target NG-RAN NodeTransparent Container field for carrying the SgNB UE X2AP ID.
 9. Anaccess and mobility management function (AMF), comprising: at least onetransceiver; and at least one processor, wherein the at least oneprocessor is configured to: receive, from a mobility management entity(MIME) for an evolved node B (eNB), a message associated with a handoverrequired message for an inter-system handover of a user equipment (UE)from an evolved packet system (EPS) to 5G system (5GS) with a secondarygNB (SgNB) used as a target next generation node B (gNB); transmit, tothe target gNB, a handover request message for the inter-system handoverfrom the EPS to 5GS with the SgNB used as the target gNB; and receive,from the target gNB, an acknowledge of the handover request message,wherein the SgNB and the target gNB are co-located in a network entity,wherein the eNB is associated with the SgNB in a dual connectivity,wherein the handover required message includes an SgNB UE X2 applicationprotocol ID (SgNB UE X2AP ID) for identifying the UE over an X2interface in the SgNB, wherein the handover request message includes theSgNB UE X2AP ID, and wherein the SgNB UE X2AP ID is allocated at theSgNB.
 10. The AMF of claim 9, wherein the SgNB and the target gNBcorresponds to a same network entity, wherein the handover requiredmessage includes a Source NG-RAN Node to Target NG-RAN Node TransparentContainer field for carrying the SgNB UE X2 application protocol ID, andwherein the handover request message includes a Source NG-RAN Node toTarget NG-RAN Node Transparent Container field for carrying the SgNB UEX2 application protocol ID.
 11. The AMF of claim 9, wherein the at leastone processor is further configured to: transmit, to the MME, a messageto transmit a handover command message from the MME to the eNB.
 12. Anetwork entity, comprising: at least one transceiver; and at least oneprocessor, wherein the at least one processor is configured to: receive,from an access and mobility management function (AMF), a handoverrequest message for an inter-system handover of a user equipment (UE)from an evolved packet system (EPS) to 5G system (5GS) with a secondarygNB (SgNB) used as a target next generation node B (gNB); and transmit,to the AMF, an acknowledge of the handover request message, wherein theSgNB and the target gNB are co-located in the network entity, whereinthe SgNB is associated with an evolved node B (eNB) in a dualconnectivity, wherein the handover request message includes SgNB UE X2application protocol ID (SgNB UE X2AP ID) for identifying the UE over anX2 interface in the SgNB, and wherein the SgNB UE X2AP ID is allocatedat the SgNB.
 13. The network entity of claim 12, wherein the at leastone processor is further configured to: if a bearer terminated at theSgNB is identified, perform a data forwarding in a node-internal way forthe bearer terminated at the SgNB.
 14. The network entity of claim 12,wherein the SgNB and the target gNB corresponds to a same networkentity, and wherein the handover request message includes a SourceNG-RAN Node to Target NG-RAN Node Transparent Container field forcarrying the SgNB UE X2 application protocol ID.
 15. An evolved node B(eNB), comprising: at least one transceiver; and at least one processor,wherein the at least one processor is configured to: transmit, to amobility management entity (MME), a handover required message for aninter-system handover a secondary gNB from an evolved packet system(EPS) to 5G system (5GS) with a secondary gNB (SgNB) used as a targetnext generation node B (gNB); and receive, from the MME, a handovercommand message, wherein the SgNB and the target gNB are co-located in anetwork entity, wherein the eNB is associated with the SgNB in a dualconnectivity, wherein the handover required message includes SgNB UE X2application protocol ID (SgNB UE X2AP ID) for identifying the UE over X2interface in the SgNB, and wherein the SgNB UE X2AP ID is allocated atthe SgNB.
 16. The eNB of claim 15, wherein the SgNB and the target gNBcorresponds to a same network entity, and wherein the handover requiredmessage includes a Source NG-RAN Node to Target NG-RAN Node TransparentContainer field for carrying the SgNB UE X2AP ID.